CODEWITHSUNDEEP
pythonlist
user1000107
user1000107

Reputation: 415

In python, how to extract some char from each item of a list ?

In python, how to extract some char from each item of a list ?

e.g. in a list, each item (modelName) has 

  cfn99e1195_1.lp

The numbers inside may be different.

I need to get 99 and 1195.

I tried 

 findN = modelName.find('n')  
 findE = modelName.find('e')
 nodeNum = modelName(findN, findE) 
 findBar = modelName.find('_')  
 arcNum = modelName(findE, findBar)

does not work.

thanks

Upvotes: 0

Views: 203

Answers (3)

Roman Susi
Roman Susi

Reputation: 4199

The groupdict could be more illustrative, also a check if the match is really there:

pattern = re.compile(r'^cfn(?P<a>\d+)e(?P<b>\d+)')
m = pattern.match('cfn99e1195_1.lp')
d = {}
if m:
    d = m.groupdict()

# the result will be in the form {'a': '99', 'b': '1195'}
# or {} if not matched

OF course, the patter could be reused for all similar matching operations.

Upvotes: 1

yak
yak

Reputation: 9041

This:

nodeNum = modelName(findN, findE)

doesn't make much sense. You're trying to call the string here as if it were a function.

What you want is this:

nodeNum = modelName[findN + 1: findE]

But remember that .find() can return -1 if the substring wasn't found.

So at the very least, replace .find() with .index() which does the same thing but raises an exception instead if the substring is not found.

You might also want to consider using regular expressions to extract the numbers.

Upvotes: 0

qiao
qiao

Reputation: 18219

consider using regular expressions:

import re

pattern = re.compile(r'^cfn(\d+)e(\d+)')
a, b = pattern.match('cfn99e1195_1.lp').groups()

Upvotes: 1

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