Question

I’m curious about the difference between lambda function and a regular function (defined with def) – in the python level. (I know what is the difference for programmers and when to use each one.)

>>> def a():
    return 1

>>> b = lambda: 1
>>> a
<function a at 0x0000000004036F98>
>>> b
<function <lambda> at 0x0000000004031588>

As we can see – python knows that b is a lambda function and a is a regular function. why is that? what is the difference between them to python?

Answer 1

They are the same type so they are treated the same way:

>>> type(a)
<type 'function'>
>>> type(b)
<type 'function'>

Python also knows that b was defined as a lambda function and it sets that as function name:

>>> a.func_name
'a'
>>> b.func_name
'<lambda>'

In other words, it influences the name that the function will get but as far as Python is concerned, both are functions which means they can be mostly used in the same way. See mgilson’s comment below for an important difference between functions and lambda functions regarding pickling.