Python: Return list result problem in a function

Question

If I do this with print function

def numberList(items):
     number = 1
     for item in items:
         print(number, item)
         number = number + 1

numberList(['red', 'orange', 'yellow', 'green'])

I get this

1 red
2 orange
3 yellow
4 green

if I then change the print function to return function I get just only this:

(1, 'red')

why is this so?

I need the return function to work exactly like the print function, what do I need to change on the code or rewrite...thanks...Pls do make your response as simple, understandable and straight forward as possible..cheers

Solution 1

return ends the function, while yield creates a generator that spits out one value at a time:

def numberList(items):
     number = 1
     for item in items:
         yield str((number, item))
         number = number + 1

item_lines = '\n'.join(numberList(['red', 'orange', 'yellow', 'green']))

alternatively, return a list:

def numberList(items):
     indexeditems = []
     number = 1
     for item in items:
         indexeditems.append(str((number, item)))
         number = number + 1
     return indexeditems

item_lines = '\n'.join(numberList(['red', 'orange', 'yellow', 'green']))

or just use enumerate:

item_lines = '\n'.join(str(x) for x in enumerate(['red', 'orange', 'yellow', 'green'], 1)))

In any case '\n'.join(str(x) for x in iterable) takes something like a list and turns each item into a string, like print does, and then joins each string together with a newline, like multiple print statements do.

Solution 2

A return function will return the value the first time it's hit, then the function exits. It will never operate like the print function in your loop.

Reference doc: http://docs.python.org/reference/simple_stmts.html#grammar-token-return_stmt

What are you trying to accomplish?

You could always return a dict that had the following:

{'1':'red','2':'orange','3':'yellow','4':'green'}

So that all elements are held in the 1 return value.

Comments

[Kolly Boy]

I understand that, what I want is stated in my question

[agf]

This doesn't help him with how to do it.

[mal-wan]

What you want is impossible unless you capture all elements in the 1 return object as I suggested or use yield as agf suggested. A return statement ends a function - it can't return multiple times.

[djhoese]

+1 for mentioning enumerate and your appending to a list solution (that's how I was going to answer it).