read only numbers from text file in python

Question

I have a text file with the following entries:

 Y-6.352 Z281.116 A3=-1.0 B3=0.0 C3=0.0

I want only the numbers of each variable as follows:

 -6.352 281.116 -1.0 0.0 0.0

Any suggestions on how to approach this? I am new to python and couldn't figure a function to work this out. Any suggestions would be appreciated

Possible duplicate of [Python: Extract numbers from a string](https://stackoverflow.com/questions/4289331/python-extract-numbers-from-a-string) — ᴀʀᴍᴀɴ, Nov 07 '17 at 15:27

Martin Evans · Answer 1 · 2017-11-07T16:34:15.400

1

So if your text file contains:

Y-6.352 Z281.116 A3=-1.0 B3=0.0 C3=0.0
Y-6.352 Z281.116 A3=-1.0 B3=0.0 C3=0.0 Y2.249 Z283.923 A3=-1.0 B3=0.0 C3=0.0

You could use the following non-regex approach:

def get_value(v):
    try:
        return float(v.split('=')[1])
    except IndexError as e:
        return float(v[1:])

with open('input.txt') as f_input:
    for raw_row in f_input:
        values = map(get_value, raw_row.split())
        print values

Giving you:

[-6.352, 281.116, -1.0, 0.0, 0.0]
[-6.352, 281.116, -1.0, 0.0, 0.0, 2.249, 283.923, -1.0, 0.0, 0.0]

edited Nov 07 '17 at 16:34

answered Nov 07 '17 at 15:45

Martin Evans

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Unfortunately all the lines are not similar. They are something like this : `Y-6.352 Z281.116 A3=-1.0 B3=0.0 C3=0.0` `Y2.249 Z283.923 A3=-1.0 B3=0.0 C3=0.0` – Prasanth Nov 07 '17 at 16:01
Then best use a function. I have updated the script. – Martin Evans Nov 07 '17 at 16:07

Keerthana Prabhakaran · Answer 2 · 2017-11-07T15:43:06.500

0

Say s is the line of your file, you can use lookbehind assertion. ?<= to check for variables!

>>> import re
>>> s
'Y-6.352 Z281.116 A3=-1.0 B3=0.0 C3=0.0'
>>> re.findall("(?<=[AZaz])?(?!\d*=)[0-9.+-]+",s)
['-6.352', '281.116', '-1.0', '0.0', '0.0']

If you want to do the same with files,

import re
with open('input file.txt','r') as file:
    for line in file:
        print re.findall("(?<=[AZaz])?(?!\d*=)[0-9.+-]+",line)

edited Nov 07 '17 at 15:43

answered Nov 07 '17 at 15:31

Keerthana Prabhakaran

3,766
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missed the first digit – Van Peer Nov 07 '17 at 15:33
1

Variables are not differentiated with `=`! I just realised. Give me a moment! – Keerthana Prabhakaran Nov 07 '17 at 15:34
@KeerthanaPrabhakaran it works partially though. My input line is just a set of values but you have taken it as a string ' '. I have a whole file with 100+ input lines like these. How to take them as a string? – Prasanth Nov 07 '17 at 15:53
This works too! >>> s='Y-342.33' >>> re.findall("(?<=[AZaz])?[0-9.+-]+",s) ['-342.33'] – Keerthana Prabhakaran Nov 07 '17 at 15:54
When you read the lines of your file, it is read as string and hence that shouldn't be a problem. Can you please share a sample IO! – Keerthana Prabhakaran Nov 07 '17 at 15:55
input: `Y-6.352 Z281.116 A3=-1.0 B3=0.0 C3=0.0` `Y2.249 Z283.923 A3=-1.0 B3=0.0 C3=0.0` output: `-6.352, 281.116, -1.0, 0.0, 0.0` `2.249, 283.923, -1.0, 0.0, 0.0` – Prasanth Nov 07 '17 at 16:06
Okay! The second code snippet does just this! It reads through the lines of file and finds the patters! – Keerthana Prabhakaran Nov 07 '17 at 16:08
Cool. If you feel if a solution answers your question, kindly accept it so that it can help someone else with a similar problem! – Keerthana Prabhakaran Nov 08 '17 at 02:38

read only numbers from text file in python

2 Answers2