What does “lambda” mean in Python, and what’s the simplest way to use it?

by

Lambda, which originated from Lambda Calculus and (AFAIK) was first implemented in Lisp, is basically an anonymous function – a function which doesn’t have a name, and is used in-line, in other words you can assign an identifier to a lambda function in a single expression as such:

>>> addTwo = lambda x: x+2
>>> addTwo(2)
4

This assigns addTwo to the anonymous function, which accepts 1 argument x, and in the function body it adds 2 to x, it returns the last value of the last expression in the function body so there’s no return keyword.

The code above is roughly equivalent to:

>>> def addTwo(x):
...     return x+2
... 
>>> addTwo(2)
4

Except you’re not using a function definition, you’re assigning an identifier to the lambda.

The best place to use them is when you don’t really want to define a function with a name, possibly because that function will only be used one time and not numerous times, in which case you would be better off with a function definition.

Example of a hash tree using lambdas:

>>> mapTree = {
...     'number': lambda x: x**x,
...     'string': lambda x: x[1:]
... }
>>> otype="number"
>>> mapTree[otype](2)
4
>>> otype="string"
>>> mapTree[otype]('foo')
'oo'

In this example I don’t really want to define a name to either of those functions because I’ll only use them within the hash, therefore I’ll use lambdas.

More Related Contents:

  1. Using lambda function in python
  2. Python 2.7.10: Using LAMBDA and LOGICAL operators in DICT to choose a case
  3. How are lambdas useful? [closed]
  4. How to understand closure in a lambda?
  5. Finding the average of a list
  6. Python lambda closure scoping
  7. Is it pythonic: naming lambdas
  8. Syntax behind sorted(key=lambda: …)
  9. List comprehension vs. lambda + filter
  10. python max function using ‘key’ and lambda expression
  11. Tkinter lambda function
  12. Can a lambda function call itself recursively in Python?
  13. Assignment inside lambda expression in Python
  14. What is key=lambda
  15. List comprehension and lambdas in Python [duplicate]
  16. E731 do not assign a lambda expression, use a def
  17. Why doesn’t print work in a lambda?
  18. lambda function don’t closure the parameter in Python? [duplicate]
  19. Lifetime of object in lambda connected to pyqtSignal
  20. Check if two Python functions are equal
  21. Use value of variable in lambda expression [duplicate]
  22. Why do parentheses in a lambda function cause syntax error on Python 3? [duplicate]
  23. Why use lambda functions?
  24. Dictionary With Lambda Values Updates All Entries
  25. Is there a way to perform “if” in python’s lambda? [duplicate]
  26. What exactly is “lambda” in Python? [duplicate]
  27. PyQt5 button lambda variable becomes boolean [duplicate]
  28. Python one-line “for” expression [duplicate]
  29. Nested lambda statements when sorting lists
  30. Creating Python function with partial parameters

Leave a Comment