Python Regex multi group pattern findall() returning empty list

Question

I am trying to use Regex multi group pattern to extract different CPU specs from a line, but getting an empty list.When i try individual groups separately, i am able to extract corresponding values. How should i use multi group pattern here? Please help!

import re

line = "R7000 CPU at 160MHz, Implementation 39, Rev 2.1, 256KB L2, 512KB L3 Cache"

pat_cpu_values_combined = r"(?P<freq>\s+\w+Hz)(?P<L2>\s+\w+\s+L2)(?P<L3>\s+\w+\s+L3)"
pat_cpu_freq = r"(?P<freq>\s+\w+Hz)"
pat_cpu_l2 = r"(?P<L2>\s+\w+\s+L2)"
pat_cpu_l3 = r"(?P<L3>\s+\w+\s+L3)"

# empty list coming when pat_cpu_values_combined is searched

print re.findall(pat_cpu_values_combined, line)

# below individual group pattern findall are working fine

print re.findall(pat_cpu_freq, line)
print re.findall(pat_cpu_l2, line)
print re.findall(pat_cpu_l3, line)

James · Accepted Answer · 2017-12-09 04:48:33Z

1

Your combined regex is looking for each of those patterns smashed together, with no intermediate characters. You can instead combine your patterns with the | separator.

pat_cpu_values_combined = r"(?P<freq>\s+\w+Hz)|(?P<L2>\s+\w+\s+L2)|(?P<L3>\s+\w+\s+L3)"

[''.join(g) for g in  re.findall(pat_cpu_values_combined, line)]
# returns:
[' 160MHz', ' 256KB L2', ' 512KB L3']

answered Dec 9, 2017 at 4:48

James

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James Over a year ago

No problem. Please remember to mark the question as answered.

Josh Withee · Accepted Answer · 2017-12-09 04:54:49Z

0

When you combine them, you are not accounting for the characters in between the things you want to match. Try using this for your combined regex:

(?P<freq>\s+\w+Hz).*?(?P<L2>\s+\w+\s+L2).*?(?P<L3>\s+\w+\s+L3)

answered Dec 9, 2017 at 4:54

Josh Withee

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Nafeez Quraishi Over a year ago

This did not work for me, with this pattern also i am getting empty list.

Galen · Accepted Answer · 2017-12-09 04:55:32Z

0

pat_cpu_values_combined expects strings matching your three individual patterns to occur with nothing in between them.

If you want to find all three in that order, use something like:

pat_cpu_values_combined = r"(?P<freq>\s+\w+Hz).*?(?P<L2>\s+\w+\s+L2).*?(?P<L3>\s+\w+\s+L3)"

answered Dec 9, 2017 at 4:55

Galen

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