如何传递参数（元组）-不同长度

Question

This question may seem very basic, however, I would like to improve the code I have written. I have a function that will need either 2 or 3 parameters, depending on some other conditions. I'm checking the length and passing either 2 or 3 with and if statement (see code). I'm sure there must be a better and compact way to re-write in one line/sentence instead of using IIFs. Sorry i'm fairly new to python.

dist = distr.gum 
# ... or: dist = distr.gev 

# parFitHist has length 2 for distr.gum or 3 for distr.gev 
parFitHist = dist.fit(ppt_hist) 

# now I check if 
if len(parFitBase) > 2: 
    # 3 parameters for distr.gev
    t_mp = dist.cdf(ppt_fut, parFitFut[0], parFitFut[1],  parFitBase[2]) 
else:
    # 2 parameters for distr.gum
    t_mp = dist.cdf(ppt_fut, parFitFut[0], parFitFut[1])  

Answer 1

Not sure what data types you have and how your method looks like, but with *args you can solve that:

def cdf(ppt_fut, *params):
    print(ppt_fut)
    print(params)

Then you can call it like that:

cdf(1, 2, 3, 4) # -> prints: 1 (2,3,4)
cdf(1, 2, 3) # -> prints: 1 (2,3)

The params is in this case a tuple with all arguments except the first one.

Answer 2

You can unpack elements of a list into a function call with * .

You don't need to know how many items there are in the list to do this. But this means you can introduce errors if the number of items don't match the function arguments. It's therefore a good idea to check your data for some basic sanity as well.

For example:

if 1 < len(parFitBase) < 4:
    t_mp = dist.cdf(ppt_fut, *parFitFut)
else:
    raise ValueError('Array must have length 2 or 3')

You can read more about that here: Unpacking Argument Lists

Answer 3

Welcome to python. Please consider using pep8 for formatting your code. It is a great way to respect conventions and make your code more readable for other people.

Variable names should be lower case and separated by underscores.

Regarding your question, one way of improving it could be to pass len(par_fit_base) to your function and doing the if clause there. This would make it more fluent to read the code. This is assuming that par_fit_fut always has the same length, regardless of par_fit_base .

def my_function(par_fit_fut, n):
    if n > 2:
        # one set of routines using par_fit_fut[0:3]
    else:
        # another set of routines using par_fit_fut[0:2]

my_function(par_fit_fut, len(par_fit_base))