How to iterate over function arguments

Question

I have a Python function accepting several string arguments def foo(a, b, c): and concatenating them in a string.
I want to iterate over all function arguments to check they are not None. How it can be done?
Is there a quick way to convert None to “”?

Thanks.

Asked By: jackhab

||

Source

Answer 1

def func(*args):
    ' '.join(i if i is not None else '' for i in args)

if you’re joining on an empty string, you could just do ''.join(i for i in args if i is not None)

Answered By: SilentGhost

Answer 2

I would use sed s/None//g, but that’s not in python, but you can probably use os.popen() to do that.

Answered By: Ernst

Answer 3

locals() may be your friend here if you call it first thing in your function.

Example 1:

>>> def fun(a, b, c):
...     d = locals()
...     e = d
...     print e
...     print locals()
... 
>>> fun(1, 2, 3)
{'a': 1, 'c': 3, 'b': 2}
{'a': 1, 'c': 3, 'b': 2, 'e': {...}, 'd': {...}}

Example 2:

>>> def nones(a, b, c, d):
...     arguments = locals()
...     print 'The following arguments are not None: ', ', '.join(k for k, v in arguments.items() if v is not None)
... 
>>> nones("Something", None, 'N', False)
The following arguments are not None:  a, c, d

Answer:

>>> def foo(a, b, c):
...     return ''.join(v for v in locals().values() if v is not None)
... 
>>> foo('Cleese', 'Palin', None)
'CleesePalin'

Update:

‘Example 1’ highlights that we may have some extra work to do if the order of your arguments is important as the dict returned by locals() (or vars()) is unordered. The function above also doesn’t deal with numbers very gracefully. So here are a couple of refinements:

>>> def foo(a, b, c):
...     arguments = locals()
...     return ''.join(str(arguments[k]) for k in sorted(arguments.keys()) if arguments[k] is not None)
... 
>>> foo(None, 'Antioch', 3)
'Antioch3'

Answered By: johnsyweb

Answer 4

You can use the inspect module and define a function like that:

import inspect
def f(a,b,c):
    argspec=inspect.getargvalues(inspect.currentframe())
    return argspec
f(1,2,3)
ArgInfo(args=['a', 'b', 'c'], varargs=None, keywords=None, locals={'a': 1, 'c': 3, 'b': 2})

in argspec there are all the info you need to perform any operation with argument passed.

To concatenate the string is sufficient to use the arg info received:

def f(a,b,c):
    argspec=inspect.getargvalues(inspect.currentframe())
    return ''.join(argspec.locals[arg] for arg in argspec.args)

For reference:
http://docs.python.org/library/inspect.html#inspect.getargvalues

Answered By: pygabriel

Answer 5

Is this perhaps what you’d like?

def foo(a, b, c):
    "SilentGhost suggested the join"
    ' '.join(i if i is not None else '' for i in vars().values())

def bar(a,b,c): 
    "A very usefull method!"
    print vars()
    print vars().values()

Notice the use of vars(), which returns a dict.

Answered By: extraneon

How to iterate over function arguments

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