Splitting a string in a list to find and replace elements in python

Question

I have a list of currency pairs, let's say for example it looks like this:

cp = ['EURUSD', 'CHFUSD', 'JPYUSD', 'CADUSD']

What I'm looking to do is iterate through this list, changing the USD to GBP to result in a new list that would display:

new_cp = ['EURGBP', 'CHFGBP', 'JPYGBP', 'CADGBP']

The way I assumed I would do it would be to loop through each pair, split the string into a list, remove the last 3 elements, and then append 'G', 'B', 'P' as the new last 3 elements, and finally returning this back in to a string, and adding it to the new list, 'new_cp'.

The code I began with was:

for pair in cp:
   split_pair = pair.split()

However, all this results in is getting:

['EURUSD']
['CHFUSD']

etc.

So it's just splitting the list, not splitting the string for each currency pair within the list.

I know this is relatively beginner stuff, but I am really stumped. I just don't get why this doesn't work.

If you can help with what I am doing wrong there, or even suggest a more efficient way to achieve what I'm looking to do that would be really appreciated.

How is .split supposed to know that you mean split into two sets of three characters? By default, it splits on any whitespace, of which there is none. — jonrsharpe
– jonrsharpe, Commented Feb 10, 2019 at 15:47
.split() without an argument, splits on whitespace, it won't magically identify you want the boundary at 'USD'/ after 3 chars- consider instead slicing the string or using .replace() — Chris_Rands
– Chris_Rands, Commented Feb 10, 2019 at 15:50
your data structure looks sub-optimal too, a list of tuples or a dict, would seem more natural e.g. [('EUR', 'USD'), ('CHF', 'USD')] etc. — Chris_Rands
– Chris_Rands, Commented Feb 10, 2019 at 15:54

Chris_Rands · Accepted Answer · 2019-02-10 15:58:35Z

5

I would suggest using the .replace() method

For example:

cp = ['EURUSD', 'CHFUSD', 'JPYUSD', 'CADUSD']
new_cp = []

for currency in cp:
    new_cp.append(currency.replace('USD', 'GBP'))

print(new_cp)

>> ['EURGBP', 'CHFGBP', 'JPYGBP', 'CADGBP']

Hope this helps :)

edited Feb 10, 2019 at 15:58

Chris_Rands

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answered Feb 10, 2019 at 15:52

Joe Tilsed

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1 Comment

balderman Over a year ago

one liner: [(currency.replace('USD', 'GBP') for currency in ['EURUSD', 'CHFUSD', 'JPYUSD', 'CADUSD']]

user5407570 · Accepted Answer · 2019-02-10 15:52:04Z

4

You could achieve this by using replace in a list comprehension:

cp = ['EURUSD', 'CHFUSD', 'JPYUSD', 'CADUSD']
new_cp = [word.replace('USD', 'GBP') for word in cp] 
#i.e.: for word in cp, we apply the specified function to it - replace the 'USD' in that word with 'GBP' - and then append it to a new list
print(new_cp)

outputs: ['EURGBP', 'CHFGBP', 'JPYGBP', 'CADGBP']

answered Feb 10, 2019 at 15:52

user5407570

Comments

Luke DeLuccia · Accepted Answer · 2019-02-10 15:55:45Z

3

If you know that each currency pair will contain USD as the last three characters, the more efficient way is to just use list indexing and append GBP:

new_cp = [i[:-3] + 'GBP' for i in cp]

answered Feb 10, 2019 at 15:55

Luke DeLuccia

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Comments

Sivaraj Velayutham · Accepted Answer · 2019-02-10 16:11:33Z

2

Here is another solution. You can use RegEx to replace the Currency values.

import re

cp = ['EURUSD', 'CHFUSD', 'JPYUSD', 'CADUSD']

mycurr = 'GBP'

to_curr = re.compile("USD")

for pair in cp:
    print(to_curr.sub(mycurr, pair))

Output:

EURGBP
CHFGBP
JPYGBP
CADGBP

answered Feb 10, 2019 at 16:11

Sivaraj Velayutham

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