Can you create a function that has custom code via parameters in python?

Question

What I mean by the title is this for ex:

def write_to_file(*params):
    with open(path, 'r+', encoding="utf-8") as file:
        content = file.read()
        file.seek(0) 

        # custom code via func parameters to be executed
        # for example *params will be ["file.write("test" + '\n')", "]
        # and here will be like for loop that goes through the params ?
        # for code in params:
            #code.execute() ?
    
        file.truncate()

Hopefully I explained it well, just wondering if you can do any of this.

// Edit (better explanation): I want to convert string into a code executable, "print(x)" -> print(x) that will be called in a function.

You can pass a function into another function and then call it. Is that what you need? — khelwood, Jan 13 '22 at 12:40
The reasonable way to do this is to have your function accept another function, i.e. a "callback" — juanpa.arrivillaga, Jan 13 '22 at 12:41
for ex.: write_to_file(["x = 1", "print(x)", "x = len(content)", "print(x)"]) — ZippoKs, Jan 13 '22 at 12:42
__Don't do this__ - https://stackoverflow.com/a/1832957/9296093 — matszwecja, Jan 13 '22 at 12:45
Or to reverse it: only do this if you are in **full** control of the incoming strings, like: you typing them yourself. Otherwise, just assume your worst personal enemy sits in front of the computer and is allowed to type in those strings to be evaluated. — GhostCat, Jan 13 '22 at 12:53
@GhostCat At this point you can just as well make it a selection of predetermined options and/or write them directly in the code. There are rare use-cases for eval, but this is __not__ one of them — matszwecja, Jan 13 '22 at 12:58

score 2 · Answer 1 · answered Jan 13 '22 at 12:43

2

pass the function itself:

def write_to_file(func):
    with open(path, 'r+', encoding="utf-8") as file:
        content = file.read()
        file.seek(0) 
        func()
        file.truncate()

def func():
    print("foo")

write_to_file(func)

answered Jan 13 '22 at 12:43

muliku

416
3
17

I didn't explain it well, my bad. I want to convert string into a code executable, "print(x)" -> print(x) in a function. – ZippoKs Jan 13 '22 at 12:46
1

Evaluating arbitrary user-input code is a terrible idea – matszwecja Jan 13 '22 at 12:47
@ZippoKs in that case you van use 'eval': `eval("print(1)")` but that's not a good practice. If you need to use it, your code needs some reevaluation – muliku Jan 13 '22 at 12:49
Yes, eval was what I'm looking for, will do more research about it, thanks guys! – ZippoKs Jan 13 '22 at 12:50

Harshit Gupta · Accepted Answer · 2022-01-13T12:56:36.823

If you just need to execute code from a string (reading the contents of a file with .read() also returns them in form of a single or multiline string), then you might simply use eval() function for the purpose.

eval() is a built-in Python function that can evaluate any expression given in it, and any errors in expressions are also thrown on console accordingly. This function just evaluates the given single-line expression, and does not support assignment and other related operators. For other purposes, you may also want to use exec() Python function.

I initially wanted to comment it, but I lack 2 reputation score for it at the time of posting it, so have to post it as an answer here.

Yes, eval was what I'm looking for, will do more research about it, thanks guys! — ZippoKs, Jan 13 '22 at 12:50

Can you create a function that has custom code via parameters in python?

2 Answers2