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.

Answer 1

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'

Answer 2

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)

Answer 3

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

Answer 4

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.

Answer 5

我会用sed s / None // g，但这不在python中，但是您可以使用os.popen（）来做到这一点。