CODEWITHSUNDEEP
pythonvariablesfor-loopindexing
booboodingding
booboodingding

Reputation: 13

Using a list index in a variable in python 3.3

I apologize in advance, I'm an absolute beginner. What I'm trying to do is have a for loop check user input against a list to see if it's contained in that list, and if it is, place the index of that list in a variable so it can be used to access an item in another list. Here is my code so far:

cust = ["Jim", "Jane", "John"]
bal = [300, 300, 300]

curCustIndex = ""
custName = input("What is your name?")
""" Let's assume the user chose "Jane" """

for i in cust:
    if custname == cust[i]:
        curCustIndex = i

Basically, what I want is for the curCustIndex to be set to an index, such as [1] for "Jane", so I can use it to correspond with an index in another list, such as the bal list. In this case, bal[1] would be the balance for "Jane." I've tried to search for an answer, but a lot of the related topics are a little too advanced for me understand. Oh, and yes, I'm intentionally using global variables. This is a beginner's python class.

Thanks in advance

Upvotes: 0

Views: 4440

Answers (3)

TheSoundDefense
TheSoundDefense

Reputation: 6935

Instead of for i in cust, use for i in range(len(cust)). That will give you the index. Simply using for i in cust will assign the actual item from your list to i, not the index of the item in the list.

Better yet, use for i, customer in enumerate(cust). When you do that, i is the index, and customer is the actual item from the list.

for i, customer in enumerate(cust):
  if custname == customer:
    curCustIndex = i

Upvotes: 0

Sylvain Leroux
Sylvain Leroux

Reputation: 51990

Python lists have an index method that returns the position of a given item:

>>> cust = ["Jim", "Jane", "John"]
>>> bal = [300, 300, 300]
>>> cust.index("John")
2
>>> bal[cust.index("John")]
300

As stated in the doc, it is an "error [to call index] if there is no such item":

>>> cust.index("Paul")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: 'Paul' is not in list

So in real code you have to wrap that in a try ... except ... block:

cust = ["Jim", "Jane", "John"]
bal = [300, 300, 300]

custName = input("What is your name?")
try:
    print(custName, "has", bal[cust.index(custName)])
except ValueError:
    print("No such client:", custName)

And testing:

sh$ python3 t.py
What is your name?John
John has 300
sh$ python3 t.py
What is your name?Paul
No such client: Paul

Upvotes: 1

zck
zck

Reputation: 2762

The function zip combines two lists into pairs of elements -- one in each pair taken from each list.

In [135]: zip([1,2,3], [4,5,6])
Out[135]: [(1, 4), (2, 5), (3, 6)]

So we can iterate over both customers and balances together.

In [136]: customers = ["Jim", "Jane", "Steve"]

In [137]: balances = [100, 987654, 31415]

In [138]: for person, balance in zip(customers, balances):
   .....:   if("J" in person):
   .....:     print("{0} has a balance of {1}".format(person, balance))
   .....: 
Jim has a balance of 100
Jane has a balance of 987654

However, you might consider using a different datatype, so you don't have to loop over all the balances. Dictionaries let you look up values by a "key", as follows:

In [140]: accounts = {"Jim": 100, "Jane": 987654, "Steve": 31415}

In [141]: accounts["Steve"]
Out[141]: 31415

Upvotes: 0

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