Python: concatented string, allow this to call a tuple

Question

In one file called say 'data' I have some tuples:

tuple1 = (1, 2, 3)
tuple2 = (4, 5, 6)

In another file, I import the data file and have a function that concatenates strings to be able to call these tuples.

import data

def string(tupleNumber):

    return 'tuple' + str(tupleNumber)

If I try and print the tuple, I get an error as string(1) is not defined in data.

print data.tuple1     # This works
print string(1)       # This also works
print data.string(1)  # This does not

The following result occurs:

(1, 2, 3)
tuple1

Traceback (most recent call last):
  File "C:/Python27/Scripts/tuplecall.py", line 10, in <module>
    print data.string(1)
AttributeError: 'module' object has no attribute 'string'

I can see why it's not working but can't think how to change string(1) to look like tuple1 when I try to call the data set.

The way I have got round this so far is to use the following code:

from data import *

def string(tupleNumber):

    return 'tuple' + str(tupleNumber)

print tuple1
print string(1)
print eval(string(1))

Which gives the results:

(1, 2, 3)
tuple1
(1, 2, 3)

However as my 'data' file has much data in it I was concerened I was wasting memory loading in each tuple with 'from data import *' when I can just call it as in the first case when I need it, but I'm obvioulsy missing something vital.

Also I have seen that eval() is not the best thing to use but so far it's all I have found that works. So if anyone is able to give me some ideas on how to improve my understanding I would be very much appreciated.

Kind regards

SNIFFY.

DSM · Accepted Answer · 2012-04-26 19:26:10Z

4

That's not really what variable names are meant for. The numbers 1 and 2 in tuple1 and tuple2 either mean something (e.g. the 1 really means "1 person" and the 2 "2 people") or they don't, they're only placeholders.

If they do mean something, you should probably use a dictionary:

>>> my_data = {1: (1,2,3), 2: (4,5,6)}
>>> my_data
{1: (1, 2, 3), 2: (4, 5, 6)}
>>> my_data[1]
(1, 2, 3)
>>> my_data[2]
(4, 5, 6)

if they don't, and you simply have two tuples, then you might as well use a list:

>>> my_data = [(1,2,3), (4,5,6)]
>>> my_data[0]
(1, 2, 3)
>>> my_data[1]
(4, 5, 6)
>>> for tup in my_data:
...     print tup
... 
(1, 2, 3)
(4, 5, 6)

You definitely don't need to use eval.

answered Apr 26, 2012 at 19:26

DSM

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1 Comment

SNIFFER_dog Over a year ago

Hi Thanks for reply, each tuple holds data for a specific case and there are about 150 cases containing 15 elements. Each case holds data that never changes so I used the tuple as it was immutable and wanted to protect the data. I have just tested with a dictionary and it works well, if you think this is a better way I will change my code. Also is it indeed better to import data using 'import data' rather than 'from data import *' in this case. If you could expand more on not needing to use eval() it would help my understanding greatly. Many thanks again, SNIFFY

Mike McMahon · Accepted Answer · 2012-04-26 19:20:15Z

0

Your method declaration for string() is not in the data file so data.string() would not work

answered Apr 26, 2012 at 19:20

Mike McMahon

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