CODEWITHSUNDEEP
pythonpython-3.xregex
kynnemall
kynnemall

Reputation: 888

Python regex find single digit if no digits before it

I have a list of strings and I want to use regex to get a single digit if there are no digits before it.

strings = ['5.8 GHz', '5 GHz']

for s in strings:
    print(re.findall(r'\d\s[GM]?Hz', s))

# output
['8 GHz']
['5 GHz']

# desired output
['5 GHz']

I want it to just return '5 GHz', the first string shouldn't have any matches. How can I modify my pattern to get the desired output?

Upvotes: 1

Views: 536

Answers (4)

Yashasvi Bhatt
Yashasvi Bhatt

Reputation: 324

Updated Answer

import re
a = ['5.8 GHz', '5 GHz', '8 GHz', '1.2', '1.2 Some Random String', '1 Some String', '1 MHz of frequency', '2 Some String in Between MHz']
res = []
for fr in a:
    if re.match('^[0-9](?=.[^0-9])(\s)[GM]Hz$', fr):
        res.append(fr)
print(res)

Output: ['5 GHz', '8 GHz']

Upvotes: 1

PieCot
PieCot

Reputation: 3629

My two cents:

selected_strings = list(filter(
    lambda x: re.findall(r'(?:^|\s+)\d+\s+(?:G|M)Hz', x),
    strings
))

With ['2 GHz', '5.8 GHz', ' 5 GHz', '3.4 MHz', '3 MHz', '1 MHz of Frequency'] as strings, here selected_strings:

['2 GHz', '   5 GHz', '3 MHz', '1 MHz of Frequency']

Upvotes: 0

JvdV
JvdV

Reputation: 75840

As per my comment, it seems that you can use:

(?<!\d\.)\d+\s[GM]?Hz\b

This matches:

  • (?<!\d\.) - A negative lookbehind to assert position is not right after any single digit and literal dot.
  • \d+ - 1+ numbers matching the integer part of the frequency.
  • [GM]?Hz - An optional uppercase G or M followed by "Hz".
  • \b - A word boundary.

Upvotes: 2

Rory Browne
Rory Browne

Reputation: 687

>>> strings = ['5.8 GHz', '5 GHz']
>>> 
>>> for s in strings:
...     match = re.match(r'^[^0-9]*([0-9] [GM]Hz)', s)
...     if match:
...         print(match.group(1))
... 
5 GHz

Upvotes: 2

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