How to add something after every number in a string in PYTHON?

Question

Say, I want to change the string 'A = (x+2.)*(y+3.)-1'

to

'A = (x+2.0e0)*(y+3.0e0)-1.0e0'.

Every number like 2. or just 2 should be changed. How to do this?

Thanks a lot!

Define "number". What should be the result of replacing this string for example: 1.2.3 4.5 6,7.8,9.a.6.c.0e891.0? — bezmax
– bezmax, Commented Mar 23, 2012 at 22:02
format of "number" will either be 2. or 2 No 1.2.3 stuff will exist in the string. Thanks — agent99
– agent99, Commented Mar 23, 2012 at 22:04

bezmax · Accepted Answer · 2012-03-23 22:16:28Z

6

Given the comment you wrote, this kind of regular expression should work:

import re

str = 'A = (x+2.)*(y+3.)-1'
print re.sub(r'(\d+)\.?',r'\1.0e0',str)

Output:

A = (x+2.0e0)*(y+3.0e0)-1.0e0

Explanation of regexp:

(...) - means capturing group, what you need to capture to reuse during replacement
\d - means any number, equivalent to [0-9]
+ - means 1 or more occurance, equivalent to {1,}
\.? - means that we want either 0 or 1 dot. ? is equivalent to {0,1}

In replacement:

\1 - means that we want to take first captured group and insert it here

edited Mar 23, 2012 at 22:16

answered Mar 23, 2012 at 22:10

bezmax

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1 Comment

bezmax Over a year ago

Added some explanation of what's going on.

Kurt Spindler · Accepted Answer · 2012-03-23 22:06:01Z

2

You're going to want to look at the re module. Specifically, re.sub(). Read through the entire documentation for that function. It can do some rather powerful things. Either that or something like a for match in re.findall() construct.

answered Mar 23, 2012 at 22:06

Kurt Spindler

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1 Comment

agent99 Over a year ago

Thanks.I've tried that but I don't know how to pass the number to the substituted output. Like, I'm able to translate 'A = x*2 + y+3' into 'A = x*something + y+something' but I'm not able to make it know the 2 and 3...

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