Looping over array of functions fails for single function in Python

Question

Consider the following piece of code:

def integ(fncts, propagate, stpSz):
    conditions = propagate.copy()
    iterator = 0
    for i in fncts:
        conditions[iterator] = conditions[iterator] + stpSz *  i(0)
        iterator+=1

    return conditions

Where fncts is an array of functions, like this:

 f1 = lambda x: x
 f2 = lambda x: 2*x
 fncts = (f1, f2)

Problem is, the code above works for length(fncts)>1. However, if there is only one function, it fails. How I can make sure the code can be executed if the user inputs only one function?

Please expand upon "it fails". Is there a traceback? If so, please add it to your question. I suspect that you are calling inteq like this integ((f1), propagate, stpSz) instead of like this integ((f1,), propagate, stpSz). Note the comma after f1. That makes it a tuple rather than just parenthesis. — Steven Rumbalski
– Steven Rumbalski, Commented Mar 14, 2012 at 14:24

Fred Foo · Accepted Answer · 2012-03-14 14:22:15Z

5

I'm assuming you mean the user inputs fncts = f? You can either require the user to always a sequence, so fncts = [f] or fncts = (f,), or check whether callable(fncts); tuples and lists are not callable.

answered Mar 14, 2012 at 14:22

Fred Foo

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2 Comments

Ingo Over a year ago

Turns out I could just solve it using if len(fncts) > 1:, but thanks for answering so I'll give you the credit!

Steven Rumbalski Over a year ago

@thomas: If checking the length of fncts works, then this answer is incorrect. All the answers here assume that you were passing a function instead of a tuple to integ. However, taking length of a function gives a TypeError (e.g. len(lambda:1), so the assumption was incorrect. Next time please ask your question more precisely and respond to requests for clarification. If something "fails" please explain the expected behavior or post a traceback. You will get better answers that way.

Silas Ray · Accepted Answer · 2012-03-14 14:22:55Z

1

Either throw an error if the first argument is not a list (at least a length 1 list) or check to see if fncts is a single function, then wrap it in a list before operating on it.

answered Mar 14, 2012 at 14:22

Silas Ray

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