Lambda

• A lambda function is a small anonymous function.
• A lambda function can take any number of arguments, but can only have one expression.
• Use lambda functions when an anonymous function is required for a short period of time.
• filter(), map() are two built-in functions that receive lambda functions as arguments.

Map():

• The map function iterates all the lists (or dictionaries etc.) and calls the lambda function for each of their element.
• The output of map() is a list which contains the result returned by the lambda function for each item it gets called.

Filter():

• The filter function iterates the list and calls the lambda function for each element.
• It returns a final list containing items for which the lambda function evaluates to True.

Reduce():

from functools import reduce

• The reduce method continuously applies a function on an iterable (such as a list) until there are no items left in the list. It produces a non-iterable result, i.e., returns a single value.

examples:

1. def fn(m, n) : return m + n
   print(reduce((lambda m, n: m + n), [1, 2, 3, 4]))
   print(reduce(fn, [1, 2, 3, 4]))
2. a = [1, 2, 3]
   x = list(map(lambda y: y + 1, a))
   print(x)
   o/p = [2, 3, 4]
3. a = [1, 2, 3]
   b = [2, 3, 4]
   x = list(map(lambda a,b: a * b, a,b))
   print(x)
   o/p = [2, 6, 12]
4. def lam(n):
   x = lambda a: a * n
   return x
   obj = lam(3)
   print(obj(2))
   o/p = 6

Reference:

1. https://www.techbeamers.com/python-lambda/