Loop function parameters for sanity check
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03-07-2019 - |
Question
I have a Python function in which I am doing some sanitisation of the input parameters:
def func(param1, param2, param3):
param1 = param1 or ''
param2 = param2 or ''
param3 = param3 or ''
This caters for the arguments being passed as None rather than empty strings. Is there an easier/more concise way to loop round the function parameters to apply such an expression to all of them. My actual function has nine parameters.
Solution
This looks like a good job for a decorator. How about this:
def sanitized(func):
def sfunc(*args, **kwds):
return func(*[arg or '' for arg in args],
**dict((k, v or '') for k,v in kwds.iteritems()))
sfunc.func_name = func.func_name
sfunc.func_doc = func.func_doc
return sfunc
You would use this on your function like so:
@sanitized
def func(param1, param2, param3):
print param1, param2, param3
Then the parameters will be replaced by the empty string if they are false:
>>> func('foo', None, 'spam')
foo spam
(Note that this will still mess up the function signature as Ned Batchelder points out in his answer. To fix that you could use Michele Simionato's decorator module-- I think you'd just need to add a @decorator
before the definition of sanitized
)
OTHER TIPS
You could do some list manipulation:
def func(param1, param2, param3):
param1, param2, param3 = map(lambda x: x or '', (param1, param2, param3))
but I'm not sure that's better than just writing out the nine lines, since once you get to nine parameters, that's a heinously long line.
You could change the declaration of the function:
def func(*args):
param1, param2, param3 = map(lambda x: x or '', args)
but then you lose the documentation that comes from having real parameter names, as well as the possibility of changing the defaults, etc. And you still have a pretty fugly line there to unpack them.
I say write out the nine lines, or change the function to have fewer parameters: nine is kind of a lot anyway!
def func(x='', y='', z='hooray!'):
print x, y, z
In [2]: f('test')
test hooray!
In [3]: f('test', 'and')
test and hooray!
In [4]: f('test', 'and', 'done!')
test and done!