Python: regular expression to find all function calls in a file but not function definition

Question

I am parsing a C code file using Python and I need to find all function calls, but not function definitions. For example:

txt = "foo(param1, bar1(foobar()), param2, !bar2(param3));"

should give me something like foo, bar1, foobar, bar2.

The regex I am using is "\w+\(" :

import re
x = re.findall("\w+\(", txt)

but then it will also match function definition like this:

text = "void foo(int param) {"

How do I modify my regex?

Tim Biegeleisen · Accepted Answer · 2020-09-25 04:18:18Z

3

You might be able to get away with using a negative lookahead in the matching pattern which asserts that no { appears in the input line:

txt = "foo(param1, bar1(foobar()), param2, !bar2(param3));"
matches = re.findall(r'(?!.*\{)\b\w+(?=\()', txt)
print(matches)

This prints:

['foo', 'bar1', 'foobar', 'bar2']

But your second input has no matches:

txt = "void foo(int param) {"
matches = re.findall(r'(?!.*\{)\b\w+(?=\()', txt)
print(matches)

This prints:

[]

answered Sep 25, 2020 at 4:18

Tim Biegeleisen

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2 Comments

hydradon Over a year ago

Thank you, i'm trying to decode your regex :) I don't get why this group (?!.*\{) stays in front but not behind.

Tim Biegeleisen Over a year ago

@hydradon The negative lookahead (?!.*\{) says to, from the very beginning of the string, assert that { does not occur anywhere later in the string (i.e. from start to end). We don't want to put this assertion later, because then it might admit some false positives.

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