empty arguments

[noob]

Hello, I've stumbled across a problem when creating a program.
The start to my program looks along the lines of:

def parseVote(s):
    if s == []:
         print('0')  

If the user doesn't input a value for parseVote() I want it to print '0' but it is missing an argument so wont do that, help would be greatly appreciated!

[buran]

You need to make the argument optional, i.e. provide default value:

def parseVote(s=None):
    if not s: # no argument or 0 or empty list/tuple as argument
        print(0)
    else:
        print(s)

In this example the default value is None, but it can be some number, e.g. 0, which will simplify the code.

def parseVote(s=0):
    print(s) # print 0 if no argument but prints empty list/tuple if supplied as argument

Note that you should not supply mutable default arguments, e.g.

def parseVote(s=[]):

THAT'S NOT THE RIGHT WAY

[noob]

You don't know how long I have messed around with this, thank you God!

[volcano63]

Note that you should not supply mutable default arguments, e.g.

def parseVote(s=[]):

THAT'S NOT THE RIGHT WAY

Actually, in some very specific cases this is the right way - if you build a caching mechanism. Though in those cases I would use underscored name.

[wavic]

*args ?

[volcano63]

What do you know - I got something right

[buran]

Yes, but that's very specific case, when this is actually desired result (i.e. you know what you are doing) and this is also mentioned in the link I provided -

When the Gotcha Isn’t a Gotcha

Sometimes you can specifically “exploit” (read: use as intended) this behavior to maintain state between calls of a function. This is often done when writing a caching function.

[volcano63]

Yes, but that's very specific case, when this is actually desired result (i.e. you know what you are doing) and this is also mentioned in the link I provided -

I followed the link after I replied.....

[micseydel]

Actually, in some very specific cases this is the right way - if you build a caching mechanism. Though in those cases I would use underscored name.

I've only ever seen it as a gotcha, including for experienced Python programmers, and have never actually seen this used for caching or anything like that (and I'd be reluctant to accept it as a good use case).

[volcano63]

I've only ever seen it as a gotcha, including for experienced Python programmers, and have never actually seen this used for caching or anything like that (and I'd be reluctant to accept it as a good use case).

Well, I have some experience, and though I've never seen it used by anyone else, I used it a couple of time. Does improving performance by 100-s of percents in resource-hogging time-critical apps count as a good cause(yes, occasionally improving performance counts, even in Python   ).

Of course, you have to keep in mind

• Cache maintenance - you may easily end up with memory leak
  
• You cannot re-assign cache - you may clean it, but you must preserve the reference
  

I am not sure if 4 years of Python (first time I used this technique couple of years ago) would define me as experienced Python programmer   , but I have some experience with programming...