David M. Synck wrote:
>Hi all,
>
>I am fairly new to Python and trying to figure out a syntax error
>concerning lists and iteration through the same. What I am trying to do is
>sum a list of float values and store the sum in a variable for use later.
>
>The relevant code looks like this -
>
>def getCredits():
>
> """ This function asks the user to input any credits not shown on their
> bank statement
>
> It returns the sum(converted to float) of the entered credits """
>
> global credits
> credlist = []
> credits = 0.0
> temp = 0.0
> print "Now you need to enter any credits not shown on your bank statement
> \n"
> print "Please enter a zero (0) once all credits have been entered \n"
> raw_input("Hit 'Enter' to continue \n")
> temp = float(raw_input("Please enter the first credit \n"))
>
> while temp != 0:
> credlist.append(temp)
> temp = float(raw_input("Please enter the next credit \n"))
>
> i = 0
> for i in credlist:
> credits += credlist[i]
> i = i + 1
>
> return credits
>
>And the syntax error I get is this -
>
>Traceback (most recent call last):
> File "./BankReconciler_Rev1.py", line 129, in ?
> main()
> File "./BankReconciler_Rev1.py", line 116, in main
> getCredits()
> File "./BankReconciler_Rev1.py", line 60, in getCredits
> credits += credlist[i]
>TypeError: list indices must be integers
>
>
>If anyone can point me in the right direction, I would greatly appreciate
>it.
>
>Thanks in advance
>
>
Your problem is here:
i = 0
for i in credlist:
credits += credlist[i]
i = i + 1
In the for loop, i is successively bound to each element in credlist
(which are floats) and you then try to index credlist with each element
in turn: you can't index lists with floats, so you get an error.
Try inserting a print command just before the credits expression, and
you'll see what I mean:
i = 0
for i in credlist:
print i
credits += credlist[i]
i = i + 1
What you probably mean is:
credits = 0.0
for i in credlist:
credits += i
However, you should really use:
credits = sum(credlist)
It's far faster and more "pythonic".
NOTE: Although it may be easy to think of Python lists as arrays,
they're more than that. The Python for loop moves through a list,
binding (think assigning) the loop variable (in this case "i") to each
*element* of the list at a time on successive iterations, viz:
>>> for i in ["apples","oranges","grapes","pears","tomatoes"]:
... print i
apples
oranges
grapes
pears
tomatoes
>>>
Hope that helps ;-)
-andyj
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