Python

Python Basics

Python Keywords (Python 3.10+)

Category	Keywords
Control Flow	if, else, elif, while, for, break, continue, pass
Boolean Logic	True, False, and, or, not, is, in
Functions	def, return, lambda, yield, global, nonlocal
Classes & OOP	class, del, self, super
Exception Handling	try, except, finally, raise, assert
Variable Control	None, as, with, from, import
Miscellaneous	await, async, match, case (Python 3.10+)
Declarations	True, False, None

import keyword
print(keyword.kwlist)

['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']

Python Functions and Tricks

What is a Function?

A function is a block of reusable code that performs a specific task. Functions help in:

• Reducing repetition (DRY principle)
• Improving readability
• Breaking large problems into smaller modules

---

Types of Functions

1. Built-in Functions: Already available in Python. 🔹 Examples: print(), len(), type(), sum(), range()

2. User-defined Functions: Functions you write yourself using def keyword.

3. Lambda Functions: Short anonymous functions created using lambda keyword.

---

Defining a Function

def greet():
    print("Hello, World!")

Calling a Function

greet()  # Output: Hello, World!

---

Function with Parameters

def greet(name):
    print(f"Hello, {name}!")

greet("Purushotham")  # Output: Hello, Purushotham!

---

Function with Return Value

def add(x, y):
    return x + y

result = add(5, 3)
print(result)  # Output: 8

---

Default Arguments

def greet(name="User"):
    print(f"Hello, {name}!")

greet()          # Output: Hello, User!
greet("AI Bro")  # Output: Hello, AI Bro!

---

Variable-Length Arguments

• *args → multiple positional arguments (tuple)
• **kwargs → multiple keyword arguments (dict)

def show_items(*args):
    for item in args:
        print(item)

show_items("Pen", "Notebook", "Pencil")

---

Lambda Functions

Short, anonymous function (used for simple operations)

square = lambda x: x**2
print(square(5))  # Output: 25

---

# Documentation (also called a docstring) is a special string that explains what a function does, its parameters, return values, and usage.

def add(a, b):
    """
    Adds two numbers.

    Parameters:
    a (int or float): First number
    b (int or float): Second number

    Returns:
    int or float: The sum of a and b
    """
    return a + b

# Accessing Documentation
print(add.__doc__)

    Adds two numbers.

    Parameters:
    a (int or float): First number
    b (int or float): Second number

    Returns:
    int or float: The sum of a and b
    

help(add)

Help on function add in module __main__:

add(a, b)
    Adds two numbers.
    
    Parameters:
    a (int or float): First number
    b (int or float): Second number
    
    Returns:
    int or float: The sum of a and b

help(str)

Help on class str in module builtins:

class str(object)
 |  str(object='') -> str
 |  str(bytes_or_buffer[, encoding[, errors]]) -> str
 |  
 |  Create a new string object from the given object. If encoding or
 |  errors is specified, then the object must expose a data buffer
 |  that will be decoded using the given encoding and error handler.
 |  Otherwise, returns the result of object.__str__() (if defined)
 |  or repr(object).
 |  encoding defaults to sys.getdefaultencoding().
 |  errors defaults to 'strict'.
 |  
 |  Methods defined here:
 |  
 |  __add__(self, value, /)
 |      Return self+value.
 |  
 |  __contains__(self, key, /)
 |      Return key in self.
 |  
 |  __eq__(self, value, /)
 |      Return self==value.
 |  
 |  __format__(self, format_spec, /)
 |      Return a formatted version of the string as described by format_spec.
 |  
 |  __ge__(self, value, /)
 |      Return self>=value.
 |  
 |  __getattribute__(self, name, /)
 |      Return getattr(self, name).
 |  
 |  __getitem__(self, key, /)
 |      Return self[key].
 |  
 |  __getnewargs__(...)
 |  
 |  __gt__(self, value, /)
 |      Return self>value.
 |  
 |  __hash__(self, /)
 |      Return hash(self).
 |  
 |  __iter__(self, /)
 |      Implement iter(self).
 |  
 |  __le__(self, value, /)
 |      Return self<=value.
 |  
 |  __len__(self, /)
 |      Return len(self).
 |  
 |  __lt__(self, value, /)
 |      Return self<value.
 |  
 |  __mod__(self, value, /)
 |      Return self%value.
 |  
 |  __mul__(self, value, /)
 |      Return self*value.
 |  
 |  __ne__(self, value, /)
 |      Return self!=value.
 |  
 |  __repr__(self, /)
 |      Return repr(self).
 |  
 |  __rmod__(self, value, /)
 |      Return value%self.
 |  
 |  __rmul__(self, value, /)
 |      Return value*self.
 |  
 |  __sizeof__(self, /)
 |      Return the size of the string in memory, in bytes.
 |  
 |  __str__(self, /)
 |      Return str(self).
 |  
 |  capitalize(self, /)
 |      Return a capitalized version of the string.
 |      
 |      More specifically, make the first character have upper case and the rest lower
 |      case.
 |  
 |  casefold(self, /)
 |      Return a version of the string suitable for caseless comparisons.
 |  
 |  center(self, width, fillchar=' ', /)
 |      Return a centered string of length width.
 |      
 |      Padding is done using the specified fill character (default is a space).
 |  
 |  count(...)
 |      S.count(sub[, start[, end]]) -> int
 |      
 |      Return the number of non-overlapping occurrences of substring sub in
 |      string S[start:end].  Optional arguments start and end are
 |      interpreted as in slice notation.
 |  
 |  encode(self, /, encoding='utf-8', errors='strict')
 |      Encode the string using the codec registered for encoding.
 |      
 |      encoding
 |        The encoding in which to encode the string.
 |      errors
 |        The error handling scheme to use for encoding errors.
 |        The default is 'strict' meaning that encoding errors raise a
 |        UnicodeEncodeError.  Other possible values are 'ignore', 'replace' and
 |        'xmlcharrefreplace' as well as any other name registered with
 |        codecs.register_error that can handle UnicodeEncodeErrors.
 |  
 |  endswith(...)
 |      S.endswith(suffix[, start[, end]]) -> bool
 |      
 |      Return True if S ends with the specified suffix, False otherwise.
 |      With optional start, test S beginning at that position.
 |      With optional end, stop comparing S at that position.
 |      suffix can also be a tuple of strings to try.
 |  
 |  expandtabs(self, /, tabsize=8)
 |      Return a copy where all tab characters are expanded using spaces.
 |      
 |      If tabsize is not given, a tab size of 8 characters is assumed.
 |  
 |  find(...)
 |      S.find(sub[, start[, end]]) -> int
 |      
 |      Return the lowest index in S where substring sub is found,
 |      such that sub is contained within S[start:end].  Optional
 |      arguments start and end are interpreted as in slice notation.
 |      
 |      Return -1 on failure.
 |  
 |  format(...)
 |      S.format(*args, **kwargs) -> str
 |      
 |      Return a formatted version of S, using substitutions from args and kwargs.
 |      The substitutions are identified by braces ('{' and '}').
 |  
 |  format_map(...)
 |      S.format_map(mapping) -> str
 |      
 |      Return a formatted version of S, using substitutions from mapping.
 |      The substitutions are identified by braces ('{' and '}').
 |  
 |  index(...)
 |      S.index(sub[, start[, end]]) -> int
 |      
 |      Return the lowest index in S where substring sub is found,
 |      such that sub is contained within S[start:end].  Optional
 |      arguments start and end are interpreted as in slice notation.
 |      
 |      Raises ValueError when the substring is not found.
 |  
 |  isalnum(self, /)
 |      Return True if the string is an alpha-numeric string, False otherwise.
 |      
 |      A string is alpha-numeric if all characters in the string are alpha-numeric and
 |      there is at least one character in the string.
 |  
 |  isalpha(self, /)
 |      Return True if the string is an alphabetic string, False otherwise.
 |      
 |      A string is alphabetic if all characters in the string are alphabetic and there
 |      is at least one character in the string.
 |  
 |  isascii(self, /)
 |      Return True if all characters in the string are ASCII, False otherwise.
 |      
 |      ASCII characters have code points in the range U+0000-U+007F.
 |      Empty string is ASCII too.
 |  
 |  isdecimal(self, /)
 |      Return True if the string is a decimal string, False otherwise.
 |      
 |      A string is a decimal string if all characters in the string are decimal and
 |      there is at least one character in the string.
 |  
 |  isdigit(self, /)
 |      Return True if the string is a digit string, False otherwise.
 |      
 |      A string is a digit string if all characters in the string are digits and there
 |      is at least one character in the string.
 |  
 |  isidentifier(self, /)
 |      Return True if the string is a valid Python identifier, False otherwise.
 |      
 |      Call keyword.iskeyword(s) to test whether string s is a reserved identifier,
 |      such as "def" or "class".
 |  
 |  islower(self, /)
 |      Return True if the string is a lowercase string, False otherwise.
 |      
 |      A string is lowercase if all cased characters in the string are lowercase and
 |      there is at least one cased character in the string.
 |  
 |  isnumeric(self, /)
 |      Return True if the string is a numeric string, False otherwise.
 |      
 |      A string is numeric if all characters in the string are numeric and there is at
 |      least one character in the string.
 |  
 |  isprintable(self, /)
 |      Return True if the string is printable, False otherwise.
 |      
 |      A string is printable if all of its characters are considered printable in
 |      repr() or if it is empty.
 |  
 |  isspace(self, /)
 |      Return True if the string is a whitespace string, False otherwise.
 |      
 |      A string is whitespace if all characters in the string are whitespace and there
 |      is at least one character in the string.
 |  
 |  istitle(self, /)
 |      Return True if the string is a title-cased string, False otherwise.
 |      
 |      In a title-cased string, upper- and title-case characters may only
 |      follow uncased characters and lowercase characters only cased ones.
 |  
 |  isupper(self, /)
 |      Return True if the string is an uppercase string, False otherwise.
 |      
 |      A string is uppercase if all cased characters in the string are uppercase and
 |      there is at least one cased character in the string.
 |  
 |  join(self, iterable, /)
 |      Concatenate any number of strings.
 |      
 |      The string whose method is called is inserted in between each given string.
 |      The result is returned as a new string.
 |      
 |      Example: '.'.join(['ab', 'pq', 'rs']) -> 'ab.pq.rs'
 |  
 |  ljust(self, width, fillchar=' ', /)
 |      Return a left-justified string of length width.
 |      
 |      Padding is done using the specified fill character (default is a space).
 |  
 |  lower(self, /)
 |      Return a copy of the string converted to lowercase.
 |  
 |  lstrip(self, chars=None, /)
 |      Return a copy of the string with leading whitespace removed.
 |      
 |      If chars is given and not None, remove characters in chars instead.
 |  
 |  partition(self, sep, /)
 |      Partition the string into three parts using the given separator.
 |      
 |      This will search for the separator in the string.  If the separator is found,
 |      returns a 3-tuple containing the part before the separator, the separator
 |      itself, and the part after it.
 |      
 |      If the separator is not found, returns a 3-tuple containing the original string
 |      and two empty strings.
 |  
 |  removeprefix(self, prefix, /)
 |      Return a str with the given prefix string removed if present.
 |      
 |      If the string starts with the prefix string, return string[len(prefix):].
 |      Otherwise, return a copy of the original string.
 |  
 |  removesuffix(self, suffix, /)
 |      Return a str with the given suffix string removed if present.
 |      
 |      If the string ends with the suffix string and that suffix is not empty,
 |      return string[:-len(suffix)]. Otherwise, return a copy of the original
 |      string.
 |  
 |  replace(self, old, new, count=-1, /)
 |      Return a copy with all occurrences of substring old replaced by new.
 |      
 |        count
 |          Maximum number of occurrences to replace.
 |          -1 (the default value) means replace all occurrences.
 |      
 |      If the optional argument count is given, only the first count occurrences are
 |      replaced.
 |  
 |  rfind(...)
 |      S.rfind(sub[, start[, end]]) -> int
 |      
 |      Return the highest index in S where substring sub is found,
 |      such that sub is contained within S[start:end].  Optional
 |      arguments start and end are interpreted as in slice notation.
 |      
 |      Return -1 on failure.
 |  
 |  rindex(...)
 |      S.rindex(sub[, start[, end]]) -> int
 |      
 |      Return the highest index in S where substring sub is found,
 |      such that sub is contained within S[start:end].  Optional
 |      arguments start and end are interpreted as in slice notation.
 |      
 |      Raises ValueError when the substring is not found.
 |  
 |  rjust(self, width, fillchar=' ', /)
 |      Return a right-justified string of length width.
 |      
 |      Padding is done using the specified fill character (default is a space).
 |  
 |  rpartition(self, sep, /)
 |      Partition the string into three parts using the given separator.
 |      
 |      This will search for the separator in the string, starting at the end. If
 |      the separator is found, returns a 3-tuple containing the part before the
 |      separator, the separator itself, and the part after it.
 |      
 |      If the separator is not found, returns a 3-tuple containing two empty strings
 |      and the original string.
 |  
 |  rsplit(self, /, sep=None, maxsplit=-1)
 |      Return a list of the substrings in the string, using sep as the separator string.
 |      
 |        sep
 |          The separator used to split the string.
 |      
 |          When set to None (the default value), will split on any whitespace
 |          character (including \n \r \t \f and spaces) and will discard
 |          empty strings from the result.
 |        maxsplit
 |          Maximum number of splits.
 |          -1 (the default value) means no limit.
 |      
 |      Splitting starts at the end of the string and works to the front.
 |  
 |  rstrip(self, chars=None, /)
 |      Return a copy of the string with trailing whitespace removed.
 |      
 |      If chars is given and not None, remove characters in chars instead.
 |  
 |  split(self, /, sep=None, maxsplit=-1)
 |      Return a list of the substrings in the string, using sep as the separator string.
 |      
 |        sep
 |          The separator used to split the string.
 |      
 |          When set to None (the default value), will split on any whitespace
 |          character (including \n \r \t \f and spaces) and will discard
 |          empty strings from the result.
 |        maxsplit
 |          Maximum number of splits.
 |          -1 (the default value) means no limit.
 |      
 |      Splitting starts at the front of the string and works to the end.
 |      
 |      Note, str.split() is mainly useful for data that has been intentionally
 |      delimited.  With natural text that includes punctuation, consider using
 |      the regular expression module.
 |  
 |  splitlines(self, /, keepends=False)
 |      Return a list of the lines in the string, breaking at line boundaries.
 |      
 |      Line breaks are not included in the resulting list unless keepends is given and
 |      true.
 |  
 |  startswith(...)
 |      S.startswith(prefix[, start[, end]]) -> bool
 |      
 |      Return True if S starts with the specified prefix, False otherwise.
 |      With optional start, test S beginning at that position.
 |      With optional end, stop comparing S at that position.
 |      prefix can also be a tuple of strings to try.
 |  
 |  strip(self, chars=None, /)
 |      Return a copy of the string with leading and trailing whitespace removed.
 |      
 |      If chars is given and not None, remove characters in chars instead.
 |  
 |  swapcase(self, /)
 |      Convert uppercase characters to lowercase and lowercase characters to uppercase.
 |  
 |  title(self, /)
 |      Return a version of the string where each word is titlecased.
 |      
 |      More specifically, words start with uppercased characters and all remaining
 |      cased characters have lower case.
 |  
 |  translate(self, table, /)
 |      Replace each character in the string using the given translation table.
 |      
 |        table
 |          Translation table, which must be a mapping of Unicode ordinals to
 |          Unicode ordinals, strings, or None.
 |      
 |      The table must implement lookup/indexing via __getitem__, for instance a
 |      dictionary or list.  If this operation raises LookupError, the character is
 |      left untouched.  Characters mapped to None are deleted.
 |  
 |  upper(self, /)
 |      Return a copy of the string converted to uppercase.
 |  
 |  zfill(self, width, /)
 |      Pad a numeric string with zeros on the left, to fill a field of the given width.
 |      
 |      The string is never truncated.
 |  
 |  ----------------------------------------------------------------------
 |  Static methods defined here:
 |  
 |  __new__(*args, **kwargs)
 |      Create and return a new object.  See help(type) for accurate signature.
 |  
 |  maketrans(...)
 |      Return a translation table usable for str.translate().
 |      
 |      If there is only one argument, it must be a dictionary mapping Unicode
 |      ordinals (integers) or characters to Unicode ordinals, strings or None.
 |      Character keys will be then converted to ordinals.
 |      If there are two arguments, they must be strings of equal length, and
 |      in the resulting dictionary, each character in x will be mapped to the
 |      character at the same position in y. If there is a third argument, it
 |      must be a string, whose characters will be mapped to None in the result.

help(list)

Help on class list in module builtins:

class list(object)
 |  list(iterable=(), /)
 |  
 |  Built-in mutable sequence.
 |  
 |  If no argument is given, the constructor creates a new empty list.
 |  The argument must be an iterable if specified.
 |  
 |  Methods defined here:
 |  
 |  __add__(self, value, /)
 |      Return self+value.
 |  
 |  __contains__(self, key, /)
 |      Return key in self.
 |  
 |  __delitem__(self, key, /)
 |      Delete self[key].
 |  
 |  __eq__(self, value, /)
 |      Return self==value.
 |  
 |  __ge__(self, value, /)
 |      Return self>=value.
 |  
 |  __getattribute__(self, name, /)
 |      Return getattr(self, name).
 |  
 |  __getitem__(...)
 |      x.__getitem__(y) <==> x[y]
 |  
 |  __gt__(self, value, /)
 |      Return self>value.
 |  
 |  __iadd__(self, value, /)
 |      Implement self+=value.
 |  
 |  __imul__(self, value, /)
 |      Implement self*=value.
 |  
 |  __init__(self, /, *args, **kwargs)
 |      Initialize self.  See help(type(self)) for accurate signature.
 |  
 |  __iter__(self, /)
 |      Implement iter(self).
 |  
 |  __le__(self, value, /)
 |      Return self<=value.
 |  
 |  __len__(self, /)
 |      Return len(self).
 |  
 |  __lt__(self, value, /)
 |      Return self<value.
 |  
 |  __mul__(self, value, /)
 |      Return self*value.
 |  
 |  __ne__(self, value, /)
 |      Return self!=value.
 |  
 |  __repr__(self, /)
 |      Return repr(self).
 |  
 |  __reversed__(self, /)
 |      Return a reverse iterator over the list.
 |  
 |  __rmul__(self, value, /)
 |      Return value*self.
 |  
 |  __setitem__(self, key, value, /)
 |      Set self[key] to value.
 |  
 |  __sizeof__(self, /)
 |      Return the size of the list in memory, in bytes.
 |  
 |  append(self, object, /)
 |      Append object to the end of the list.
 |  
 |  clear(self, /)
 |      Remove all items from list.
 |  
 |  copy(self, /)
 |      Return a shallow copy of the list.
 |  
 |  count(self, value, /)
 |      Return number of occurrences of value.
 |  
 |  extend(self, iterable, /)
 |      Extend list by appending elements from the iterable.
 |  
 |  index(self, value, start=0, stop=9223372036854775807, /)
 |      Return first index of value.
 |      
 |      Raises ValueError if the value is not present.
 |  
 |  insert(self, index, object, /)
 |      Insert object before index.
 |  
 |  pop(self, index=-1, /)
 |      Remove and return item at index (default last).
 |      
 |      Raises IndexError if list is empty or index is out of range.
 |  
 |  remove(self, value, /)
 |      Remove first occurrence of value.
 |      
 |      Raises ValueError if the value is not present.
 |  
 |  reverse(self, /)
 |      Reverse *IN PLACE*.
 |  
 |  sort(self, /, *, key=None, reverse=False)
 |      Sort the list in ascending order and return None.
 |      
 |      The sort is in-place (i.e. the list itself is modified) and stable (i.e. the
 |      order of two equal elements is maintained).
 |      
 |      If a key function is given, apply it once to each list item and sort them,
 |      ascending or descending, according to their function values.
 |      
 |      The reverse flag can be set to sort in descending order.
 |  
 |  ----------------------------------------------------------------------
 |  Class methods defined here:
 |  
 |  __class_getitem__(...)
 |      See PEP 585
 |  
 |  ----------------------------------------------------------------------
 |  Static methods defined here:
 |  
 |  __new__(*args, **kwargs)
 |      Create and return a new object.  See help(type) for accurate signature.
 |  
 |  ----------------------------------------------------------------------
 |  Data and other attributes defined here:
 |  
 |  __hash__ = None

help(dict)

Help on class dict in module builtins:

class dict(object)
 |  dict() -> new empty dictionary
 |  dict(mapping) -> new dictionary initialized from a mapping object's
 |      (key, value) pairs
 |  dict(iterable) -> new dictionary initialized as if via:
 |      d = {}
 |      for k, v in iterable:
 |          d[k] = v
 |  dict(**kwargs) -> new dictionary initialized with the name=value pairs
 |      in the keyword argument list.  For example:  dict(one=1, two=2)
 |  
 |  Built-in subclasses:
 |      StgDict
 |  
 |  Methods defined here:
 |  
 |  __contains__(self, key, /)
 |      True if the dictionary has the specified key, else False.
 |  
 |  __delitem__(self, key, /)
 |      Delete self[key].
 |  
 |  __eq__(self, value, /)
 |      Return self==value.
 |  
 |  __ge__(self, value, /)
 |      Return self>=value.
 |  
 |  __getattribute__(self, name, /)
 |      Return getattr(self, name).
 |  
 |  __getitem__(...)
 |      x.__getitem__(y) <==> x[y]
 |  
 |  __gt__(self, value, /)
 |      Return self>value.
 |  
 |  __init__(self, /, *args, **kwargs)
 |      Initialize self.  See help(type(self)) for accurate signature.
 |  
 |  __ior__(self, value, /)
 |      Return self|=value.
 |  
 |  __iter__(self, /)
 |      Implement iter(self).
 |  
 |  __le__(self, value, /)
 |      Return self<=value.
 |  
 |  __len__(self, /)
 |      Return len(self).
 |  
 |  __lt__(self, value, /)
 |      Return self<value.
 |  
 |  __ne__(self, value, /)
 |      Return self!=value.
 |  
 |  __or__(self, value, /)
 |      Return self|value.
 |  
 |  __repr__(self, /)
 |      Return repr(self).
 |  
 |  __reversed__(self, /)
 |      Return a reverse iterator over the dict keys.
 |  
 |  __ror__(self, value, /)
 |      Return value|self.
 |  
 |  __setitem__(self, key, value, /)
 |      Set self[key] to value.
 |  
 |  __sizeof__(...)
 |      D.__sizeof__() -> size of D in memory, in bytes
 |  
 |  clear(...)
 |      D.clear() -> None.  Remove all items from D.
 |  
 |  copy(...)
 |      D.copy() -> a shallow copy of D
 |  
 |  get(self, key, default=None, /)
 |      Return the value for key if key is in the dictionary, else default.
 |  
 |  items(...)
 |      D.items() -> a set-like object providing a view on D's items
 |  
 |  keys(...)
 |      D.keys() -> a set-like object providing a view on D's keys
 |  
 |  pop(...)
 |      D.pop(k[,d]) -> v, remove specified key and return the corresponding value.
 |      
 |      If the key is not found, return the default if given; otherwise,
 |      raise a KeyError.
 |  
 |  popitem(self, /)
 |      Remove and return a (key, value) pair as a 2-tuple.
 |      
 |      Pairs are returned in LIFO (last-in, first-out) order.
 |      Raises KeyError if the dict is empty.
 |  
 |  setdefault(self, key, default=None, /)
 |      Insert key with a value of default if key is not in the dictionary.
 |      
 |      Return the value for key if key is in the dictionary, else default.
 |  
 |  update(...)
 |      D.update([E, ]**F) -> None.  Update D from dict/iterable E and F.
 |      If E is present and has a .keys() method, then does:  for k in E: D[k] = E[k]
 |      If E is present and lacks a .keys() method, then does:  for k, v in E: D[k] = v
 |      In either case, this is followed by: for k in F:  D[k] = F[k]
 |  
 |  values(...)
 |      D.values() -> an object providing a view on D's values
 |  
 |  ----------------------------------------------------------------------
 |  Class methods defined here:
 |  
 |  __class_getitem__(...)
 |      See PEP 585
 |  
 |  fromkeys(iterable, value=None, /)
 |      Create a new dictionary with keys from iterable and values set to value.
 |  
 |  ----------------------------------------------------------------------
 |  Static methods defined here:
 |  
 |  __new__(*args, **kwargs)
 |      Create and return a new object.  See help(type) for accurate signature.
 |  
 |  ----------------------------------------------------------------------
 |  Data and other attributes defined here:
 |  
 |  __hash__ = None

Higher-Order Functions

A Higher-Order Function is a function that:

1. Takes one or more functions as arguments, and/or
2. Returns a function as its result

In short:

"Functions that work with other functions."

---

Examples of Higher-Order Functions in Python

---

1. Passing a Function as an Argument

def greet(name):
    return f"Hello, {name}!"

def call_func(func, value):
    return func(value)

print(call_func(greet, "Purushotham"))
# Output: Hello, Purushotham!

---

2. Returning a Function from Another Function

def outer(x):
    def inner(y):
        return x + y
    return inner

add5 = outer(5)
print(add5(10))  # Output: 15

---

Built-in Higher-Order Functions

Python provides several built-in higher-order functions:

---

map(function, iterable)

Applies a function to every item in an iterable.

nums = [1, 2, 3, 4]
squares = list(map(lambda x: x**2, nums))
print(squares)  # Output: [1, 4, 9, 16]

---

filter(function, iterable)

Filters items where the function returns True.

nums = [1, 2, 3, 4, 5]
evens = list(filter(lambda x: x % 2 == 0, nums))
print(evens)  # Output: [2, 4]

---

reduce(function, iterable)

Applies a function cumulatively to reduce the iterable to a single value.

Requires:

from functools import reduce

from functools import reduce
nums = [1, 2, 3, 4]
product = reduce(lambda x, y: x * y, nums)
print(product)  # Output: 24

---

Combine Them:

from functools import reduce

nums = [1, 2, 3, 4, 5]

# Filter even numbers, square them, then sum the result
result = reduce(lambda x, y: x + y,
                map(lambda x: x**2,
                    filter(lambda x: x % 2 == 0, nums)))

print(result)  # Output: 20 (2² + 4² = 4 + 16)

---

Python Advanced Functions

1. Function Decorators (@decorator)

A decorator modifies or enhances the behavior of a function without changing its code.

Basic Decorator

def my_decorator(func):
    def wrapper():
        print("Before call")
        func()
        print("After call")
    return wrapper

@my_decorator
def say_hello():
    print("Hello!")

say_hello()

---

2. Closures (Function inside function)

A closure remembers the environment in which it was created.

def outer(x):
    def inner(y):
        return x + y
    return inner

add5 = outer(5)
print(add5(3))  # Output: 8

---

3. First-Class Functions

In Python, functions can be:

• Assigned to variables
• Passed as arguments
• Returned from other functions

def shout(text):
    return text.upper()

def whisper(text):
    return text.lower()

def greet(func):
    print(func("Hello"))

greet(shout)
greet(whisper)

---

4. *args and `kwargs` - Advanced Use**

def demo(*args, **kwargs):
    print("Positional:", args)
    print("Keyword:", kwargs)

demo(1, 2, 3, name="Purushotham", job="ML")

---

5. Partial Functions (functools.partial)

Fix certain arguments of a function and generate a new function.

from functools import partial

def power(base, exponent):
    return base ** exponent

square = partial(power, exponent=2)
print(square(5))  # Output: 25

---

6. Anonymous Functions (Lambda with map, filter, reduce)

from functools import reduce

nums = [1, 2, 3, 4]

# map: apply function to each item
squares = list(map(lambda x: x**2, nums))

# filter: filter elements
even = list(filter(lambda x: x % 2 == 0, nums))

# reduce: accumulate results
product = reduce(lambda x, y: x * y, nums)

---

7. Generator Functions (yield)

Efficient memory handling for large sequences.

def count_up_to(n):
    i = 1
    while i <= n:
        yield i
        i += 1

for num in count_up_to(5):
    print(num)

---

8. Function Annotations (Type Hints)

Improves readability and debugging.

def greet(name: str) -> str:
    return f"Hello, {name}"

---

9. Introspection Tools

Use built-in tools to examine functions:

def sample(x: int) -> int:
    return x * 2

print(sample.__name__)
print(sample.__annotations__)
print(callable(sample))

---

10. Function Caching (Memoization)

from functools import lru_cache

@lru_cache(maxsize=1000)
def fib(n):
    if n < 2:
        return n
    return fib(n-1) + fib(n-2)

---

Python OOPS

Object-Oriented Programming (OOP) is a programming paradigm centered around objects and classes. Python supports OOP and allows you to model real-world entities.

---

Key OOP Concepts in Python

Concept	Description
Class	Blueprint for creating objects
Object	Instance of a class
Constructor	__init__ method used to initialize objects
Encapsulation	Hiding internal data using access specifiers (_, __)
Abstraction	Hiding unnecessary implementation details
Inheritance	One class (child) inherits properties from another (parent)
Polymorphism	Ability to take many forms (method overriding/overloading)

---

1. Class and Object

class Car:
    def __init__(self, brand, color):
        self.brand = brand
        self.color = color

    def drive(self):
        print(f"{self.color} {self.brand} is driving.")

my_car = Car("Toyota", "Red")
my_car.drive()  # Output: Red Toyota is driving.

---

2. Encapsulation

Protecting internal data.

class BankAccount:
    def __init__(self, balance):
        self.__balance = balance  # private variable

    def get_balance(self):
        return self.__balance

acc = BankAccount(5000)
print(acc.get_balance())  # ✅ 5000
# print(acc.__balance)   # ❌ Error: private attribute

---

3. Inheritance

Child class inherits from parent.

class Animal:
    def sound(self):
        print("Some sound")

class Dog(Animal):
    def sound(self):
        print("Bark")

d = Dog()
d.sound()  # Output: Bark

---

4. Polymorphism

Same method name, different behavior.

class Bird:
    def speak(self):
        print("Tweet")

class Parrot(Bird):
    def speak(self):
        print("Squawk")

def make_sound(bird):
    bird.speak()

make_sound(Parrot())  # Output: Squawk

---

5. Abstraction

Hide implementation, show interface (via abstract classes).

from abc import ABC, abstractmethod

class Shape(ABC):
    @abstractmethod
    def area(self):
        pass

class Circle(Shape):
    def __init__(self, radius):
        self.radius = radius

    def area(self):
        return 3.14 * self.radius ** 2

c = Circle(5)
print(c.area())  # Output: 78.5

---

🔁 Summary Table

Concept	Python Feature
Class/Object	class, __init__, object
Inheritance	class Child(Parent)
Polymorphism	Method Overriding
Encapsulation	_protected, __private vars
Abstraction	ABC, abstractmethod

---

• https://www.tutorialspoint.com/python/pdf/python_classes_objects.pdf

Python File Handling

Python allows us to create, read, write, and delete files using built-in functions like open(), read(), write(), and close().

---

Syntax: open()

file = open("filename.txt", "mode")

Common modes:

Mode	Description
'r'	Read (default), file must exist
'w'	Write, creates or overwrites
'a'	Append, creates if not exists
'x'	Exclusive create, fails if exists
'b'	Binary mode (rb, wb, etc.)
't'	Text mode (default, used with others)

---

Reading a File

# Read entire content
with open("sample.txt", "r") as f:
    content = f.read()
    print(content)

# Read line by line
with open("sample.txt", "r") as f:
    for line in f:
        print(line.strip())

# Read specific number of characters
with open("sample.txt", "r") as f:
    print(f.read(5))  # Reads 5 characters

---

Writing to a File

# Overwrites the file if it exists
with open("output.txt", "w") as f:
    f.write("Hello, world!\n")
    f.write("Second line.\n")

---

Appending to a File

with open("output.txt", "a") as f:
    f.write("This line will be added.\n")

---

Creating a New File

# Fails if the file already exists
with open("newfile.txt", "x") as f:
    f.write("Created new file.")

---

Deleting a File

import os

if os.path.exists("oldfile.txt"):
    os.remove("oldfile.txt")
else:
    print("File does not exist")

---

Checking File/Folder Existence

import os

print(os.path.exists("myfile.txt"))     # True/False
print(os.path.isfile("myfile.txt"))     # True if file
print(os.path.isdir("myfolder"))        # True if folder

---

File Object Methods

Method	Description
read()	Reads entire file
readline()	Reads a single line
readlines()	Returns list of lines
write()	Writes to file
writelines()	Writes list of strings
close()	Closes the file

Note: Use with open(...) to auto-close the file.

---

Python Exception Handling

What is Exception Handling?

Exception: An error that occurs during the execution of a program, disrupting the normal flow.

Why use it?

To gracefully handle errors and keep the program from crashing.

---

Basic Syntax

try:
    # Code that may raise an exception
    x = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero.")
else:
    print("No exceptions occurred.")
finally:
    print("Always runs.")

---

Key Blocks in Exception Handling

Block	Purpose
try	Code that may raise an exception
except	Block to catch and handle exceptions
else	Runs only if no exception occurs
finally	Runs no matter what (used for cleanup like closing files/db)

---

Catching Multiple Exceptions

try:
    x = int("abc")
except (ValueError, TypeError) as e:
    print(f"Error occurred: {e}")

---

Generic Exception Handling

Not recommended unless you're logging or debugging.

try:
    something()
except Exception as e:
    print("Error:", e)

---

Raising Exceptions

You can raise exceptions manually using raise.

def divide(a, b):
    if b == 0:
        raise ValueError("Denominator cannot be zero.")
    return a / b

---

Common Built-in Exceptions in Python

Exception	Description
ZeroDivisionError	Division by zero
ValueError	Wrong value (e.g., int('abc'))
TypeError	Operation on incompatible types
IndexError	Index out of range (e.g., list[10])
KeyError	Accessing a missing dictionary key
FileNotFoundError	File not found during file operations
AttributeError	Invalid attribute access
ImportError	Error in importing module
NameError	Variable not defined
StopIteration	Raised by next() in loops when no item exists
KeyboardInterrupt	Interrupt by user using Ctrl+C
MemoryError	Out of memory
AssertionError	When assert statement fails

---

Example: Handling File Errors

try:
    f = open("data.txt")
    content = f.read()
except FileNotFoundError:
    print("File not found.")
finally:
    print("Operation complete.")

---

Custom Exceptions

You can define your own error types by extending Exception.

class MyCustomError(Exception):
    pass

raise MyCustomError("Something went wrong.")

---

Summary Diagram

try:
    risky_code()
except SpecificError:
    handle_it()
except AnotherError as e:
    handle_with_info(e)
else:
    no_errors()
finally:
    always_runs()

---

class TooYoungError(Exception):
    pass

def register(age):
    if age < 18:
        raise TooYoungError("Must be 18+ to register.")

try:
    register(16)
except TooYoungError as e:
    print(e)

Debugging in Python

Debugging is the process of finding and fixing errors (bugs) in code.

---

1. Assertions

What are Assertions?

Assertions are used to check if a condition is True at a specific point in the program. If it’s False, Python throws an AssertionError.

assert condition, "Optional error message"

Example:

x = 5
assert x > 0, "x must be positive"

If x = -1, this will raise:

AssertionError: x must be positive

Used to catch logic errors early during development.

Don’t use assertions for user input validation in production — they can be disabled with python -O.

---

2. Traceback as a String

What is Traceback?

A traceback is the stack trace showing where an error occurred.

How to capture it as a string?

Use the traceback module:

import traceback

try:
    1 / 0
except ZeroDivisionError:
    tb_str = traceback.format_exc()
    print("Traceback as string:\n", tb_str)

Why use it?

• Useful for logging errors
• Send error details in a response (e.g., web API)
• Store for debugging later

---

3. Logging in Python

What is Logging?

A flexible system for recording:

• Errors
• Warnings
• Info
• Debug messages

More powerful and configurable than print().

---

Basic Logging Setup

import logging

logging.basicConfig(level=logging.INFO)
logging.info("This is an info message.")
logging.warning("This is a warning.")
logging.error("Something went wrong.")

---

Logging Levels

Level	Use Case
DEBUG	Detailed debugging info
INFO	General app flow messages
WARNING	Something unexpected happened
ERROR	A serious problem occurred
CRITICAL	Very serious error

---

Log to a File

logging.basicConfig(
    filename='app.log',
    level=logging.DEBUG,
    format='%(asctime)s - %(levelname)s - %(message)s'
)
logging.error("This goes to a file!")

---

Logging with Tracebacks

try:
    1 / 0
except ZeroDivisionError:
    logging.exception("Exception occurred")

This prints both error message and full traceback!

---

import logging

logging.basicConfig(level=logging.INFO)
logging.info("This is an info message.")
logging.warning("This is a warning.")
logging.error("Something went wrong.")

WARNING:root:This is a warning.
ERROR:root:Something went wrong.

logging.basicConfig(
    filename='app.log',
    level=logging.DEBUG,
    format='%(asctime)s - %(levelname)s - %(message)s'
)
logging.error("This goes to a file!")

ERROR:root:This goes to a file!

Python Modules

What is a Python Module?

A module is simply a Python file (.py) containing variables, functions, classes, etc., that you can import and reuse in other Python programs.

Purpose: Helps organize code, improve reusability, and maintainability.

---

Types of Modules

Type	Example
Built-in	math, os, sys, random
User-defined	Your own .py files
Third-party	Installed via pip like numpy, pandas, requests

---

Using Built-in Modules

Example: math

import math

print(math.sqrt(25))        # 5.0
print(math.pi)              # 3.141592653589793

---

Creating Your Own Module

File: mymodule.py

# mymodule.py
def greet(name):
    return f"Hello, {name}!"

pi = 3.14

Now use it in another file:

import mymodule

print(mymodule.greet("Purushotham"))
print(mymodule.pi)

---

import Variants

# import whole module
import math
math.sqrt(16)

# import specific function
from math import sqrt
sqrt(16)

# import with alias
import math as m
m.sqrt(16)

# import all (not recommended)
from math import *

---

Using __name__ == "__main__"

# module_test.py
def run():
    print("Running test...")

if __name__ == "__main__":
    run()

This ensures the block only runs if file is executed directly, not when imported.

---

Useful Built-in Modules

Module	Use Case
math	Mathematical operations
random	Random number generation
datetime	Date and time manipulation
os	OS-level operations (files, dirs)
sys	Command line args, interpreter info
json	Work with JSON data
re	Regular expressions
time	Timing, sleep functions

---

Third-party Modules (via pip install)

pip install requests

import requests

response = requests.get("https://api.github.com")
print(response.status_code)

---

Best Practices

• Use aliases (import numpy as np) for readability.
• Keep reusable code in modules.
• Avoid wildcard imports (from module import *) in production.
• Group all imports at the top of the file.

---

Real-world Use Case

Project: Weather App

• main.py: user interface
• weather.py: handles API requests
• utils.py: helper functions (formatting, error handling)

All parts communicate via module imports.

---