How do you read a lambda function as a string?

Question

I'd like to read a lambda function I created as a string, after I created it.

For example,

func = lambda num1,num2: num1 + num2

I'd like to read func as:

'lambda num1,num2: num1 + num2'

Is there a way to accomplish this or even read any part of the lambda function?

maccartm · Accepted Answer · 2015-06-22T15:44:18.687

13

Edit: Changed my first answer as I misunderstood the question. This answer is borrowed from a number of other uses, however I have completed the code to only display the part of the string that you want.

import inspect

func = lambda num1,num2: num1 + num2
funcString = str(inspect.getsourcelines(func)[0])
funcString = funcString.strip("['\\n']").split(" = ")[1]
print funcString

Outputs the following string:

lambda num1,num2: num1 + num2

edited Jun 22 '15 at 15:44

answered Jun 22 '15 at 15:31

maccartm

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If I copy and paste the code above I get an error at line 3: Traceback (most recent call last): File "", line 1, in File "/usr/lib/python3.9/inspect.py", line 1006, in getsourcelines lines, lnum = findsource(object) File "/usr/lib/python3.9/inspect.py", line 835, in findsource raise OSError('could not get source code') OSError: could not get source code – Siderius Dec 03 '21 at 16:26
1

Sorry for the delayed reply. @Siderius try running the code from a file instead of an interpreter. – maccartm Dec 15 '21 at 14:47

score 6 · Answer 2 · edited Dec 03 '21 at 20:58

6

You can use getsourcelines from the inspect module to do this

This function returns as a list all of the lines of the definition of any function, module, class or method as well as the line number at which it was defined.

For example:

import inspect

f = lambda x, y : x + y

print inspect.getsourcelines(f)[0][0]

Will output the definition of the function as:

f = lambda x, y: x + y

edited Dec 03 '21 at 20:58

wjandrea

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answered Jun 22 '15 at 15:32

Simon Gibbons

6,969
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score 2 · Answer 3 · answered Jun 22 '15 at 15:30

2

You can use Python's eval() function:

>>> func = eval('lambda num1,num2: num1 + num2')
>>> func
<function <lambda> at 0x7fe87b74b668>

To evaluate any expression and return the value.

answered Jun 22 '15 at 15:30

Kaiting Chen

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eval is evil and considered bad practice... advise against it. – TMOTTM Jun 07 '19 at 13:45
Also this is the opposite of the desired solution, OP is looking to get the string from the lambda, not create the lambda from the string. – mirrorcoloured Aug 23 '23 at 20:09

albert · Answer 4 · 2015-06-22T15:59:38.153

You can use Python's inspect module to get the desired code as a list of strings:

#!/usr/bin/env python3
# coding: utf-8

import inspect

func = lambda num1, num2: num1 + num2

def f():
    a = 1
    b = 2
    return a + b

def get_code_as_string(passed_func):
    return inspect.getsourcelines(passed_func)


if __name__ == '__main__':
    # feed a lambda function
    print(get_code_as_string(func))

    #feed a normal function
    print(get_code_as_string(f))

The output is as follows:

(['func = lambda num1, num2: num1 + num2\n'], 6)
(['def f():\n', '    a = 1\n', '    b = 2\n', '    return a + b\n'], 8)

As you can see inspect.getsourcelines() returns a tuple of a list and an integer. The list contains all the lines of the function passed to inspect.getsourcelines() and the integer represents the line number in which the provided functions starts.

How do you read a lambda function as a string?

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