Question

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Line continuation for list comprehensions or generator expressions in python

What is the the most pythonic way to write a long list comprehension? This list comprehension comes out to 145 columns:

memberdef_list = [elem for elem in from_cache(classname, 'memberdefs') if elem.argsstring != '[]' and 'std::string' in null2string(elem.vartype)]

How should it look if I break it into multiple lines? I couldn’t find anything about this in the Python style guides.

Answer 1

PEP 8 kinda predates list comprehensions. I usually break these up over multiple lines at logical locations:

memberdef_list = [elem for elem in from_cache(classname, 'memberdefs')
                  if elem.argsstring != '[]' and 
                     'std::string' in null2string(elem.vartype)]

Mostly though, I’d forgo the involved test there in the first place:

def stdstring_args(elem):
    if elem.argstring == '[]':
        return False
    return 'std::string' in null2string(elem.vartype)

memberdef_list = [elem for elem in from_cache(classname, 'memberdefs')
                  if stdstring_args(elem)]