Hi There, In this post we’ll learn about lambda and other built-in functions in pytrhon.

Lambda functions:

• A lambda function is a small anonymous function (function without a name).
• A lambda function can take any number of arguments, but can only have one expression.

• As we already know that def keyword is used to define the normal functions and the lambda keyword is used to create anonymous functions. It has the following syntax:

    lambda arguments: expression
  

• Example usage:

    >>> def add(a, b, c):
    ...     return a + b + c
    ...
    >>> add(1, 2, 3)
    6
    >>>
  

• The above example is a normal function which is having only return statement. We can implement the above add operation using labmada function.

    >>> add = lambda a, b, c: a + b + c
    >>>
    >>> add(1, 2, 3)
    6
    >>>
  

• In the above example a, b, c before ‘:’ are the parameters and a + b + c is the expression.

Why to use lambda functions?

• The power of lambda is better shown when you use them as an anonymous function inside another function.

map function:

• map is a standard function that accepts at least two arguments, a function and an iterable (list, sring).

• Syntax:

    res = map(function, iterable)
  

• Example usage:

    #Printing the names in all capital letters
  
    >>> avengers = ['tony', 'star loard', 'thor', 'steve', 'groot']
    >>>
    >>> result = map(lambda name: name.upper(), avengers)
    >>>
    >>> result
    <map object at 0x00680CB0>
    >>>
    >>> list(result)
    ['TONY', 'STAR LOARD', 'THOR', 'STEVE', 'GROOT']
    >>>
  

filter function:

• The filter() method filters the given sequence with the help of a function that tests each element in the sequence to be true or not.

• Syntax:

    filter(function, iterable)
  

• function - function that tests if elements of an iterable returns true or false If None, the function defaults to Identity function - which returns false if any elements are false

• iterable - iterable which is to be filtered, could be sets, lists, tuples, or containers of any iterators

• Example usage:

    #Printing the names that starts with letter a
  
    >>> a_names  = filter(lambda name: name[0] == 'a', names)
    >>>
    >>> a_names
    <filter object at 0x00680E90>
    >>>
    >>> list(a_names)
    ['alex', 'akon', 'aviry']
    >>>
  

any() and all():

• any()

• Takes one argument and the argument should be an iterable i.e list, tuple
• Returns True if any item in the list is True

• Returns False if all items in list are False

• Example usage:

    >>> any([True, False, True])
    True
    >>>
    >>> any((False, False, False))
    False
    >>>
  

• all()

• Takes one argument and the argument should be an iterable i.e list, tuple
• Returns True if all item in the list is True

• Returns False if any items in list are False

• Example usage:

    >>> all([True, False, True])
    False
    >>> all((True, True, True))
    True
    >>>
  

sorted():

• The sorted() method sorts the elements of a given iterable in a specific order - Ascending or Descending.

• syntax:

    sorted(iterable[, key][, reverse])
  

• sorted() takes two three parameters and returns a sorted list from the given iterable:
• iterable - sequence (string, tuple, list) or collection (set, dictionary, frozen set) or any iterator
• reverse (Optional) - If true, the sorted list is reversed (or sorted in Descending order)

• key (Optional) - function that serves as a key for the sort comparison

• Example usage-1:

    >>> a = [1, 3, 4, 6, 7]
    >>>
    >>> sorted(a)
    [1, 3, 4, 6, 7]
    >>> sorted(a, reverse=True)
    [7, 6, 4, 3, 1]
  

• Example usage-2:

    #Sorting by key name in list of dict
    >>> names = [{'name': 'rock'}, {'name': 'aviry'}, {'name': 'ellen'}]
    >>>
    >>> sorted(names, key=lambda name: name['name'])
    [{'name': 'aviry'}, {'name': 'ellen'}, {'name': 'rock'}]
    >>>
  

zip():

• The zip() function take iterables (can be zero or more), makes iterator that aggregates elements based on the iterables passed, and returns an iterator of tuples.

• syntax:

    zip(*iterables)
  

• iterables - can be built-in iterables (like: list, string, dict)

• If no parameters are passed, zip() returns an empty iterator

• Example:

    >>> names = ['rob', 'tony', 'john', 'alex']
    >>>
    >>> ages = ['23', '24', '30', 29]
    >>>
    >>> res = zip(names, ages)
    >>> list(res)
    [('rob', '23'), ('tony', '24'), ('john', '30'), ('alex', 29)]
    >>>