print the code which defined a lambda function [duplicate]

As long as you save your code to a source file you can retrieve the source code of an object using the inspect module.

example: open editor type:

myfunction = lambda x: x==2

save as lamtest.py

open shell type python to get to interactive python type the following:

>>>from lamtest import myfunc
>>>import inspect
>>>inspect.getsource(myfunc)

the result:

'myfunc = lambda x: x==2\n'

It will only work for mathematical based operations, but you might look at SymPy's Lambda() object. It was designed exactly for this purpose:

>>> from sympy import *
>>> x = Symbol('x')
>>> l = Lambda(x, x**2)
>>> l
Lambda(_x, _x**2)
>>> l(3)
9

It even supports pretty printing:

>>> pprint(l)
 ⎛    2⎞
Λ⎝x, x ⎠

To do your equals example, us the SymPy Eq() object:

>>> l1 = Lambda(x, Eq(x, 2))
>>> l1
Lambda(_x, _x == 2)
>>> l1(2)
True

It supports partial argument expansion:

>>> y = Symbol('y')
>>> l2 = Lambda((x, y), x*y + x)
>>> l2(1)
Lambda(_y, 1 + _y)
>>> l2(1, 2)
3

And of course, you get the advantage of getting all of SymPy's computer algebra:

>>> l3 = Lambda(x, sin(x*pi/3))
>>> pprint(l3(1))
  ⎽⎽⎽
╲╱ 3 
─────
  2

By the way, if this sounds like a shameless plug, it's because it is. I am one of the developers of SymPy.

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