python regex match and replace beginning and end of string but keep the middle

Question

I have a dataframe with holiday names. I have a problem that on some days, holidays are observed on different days, sometimes on the day of another holiday. Here are some example problems:

1  "Independence Day (Observed)"
2  "Christmas Eve, Christmas Day (Observed)"
3  "New Year's Eve, New Year's Day (Observed)"
4  "Martin Luther King, Jr. Day"

I want to replace all ' (Observed)' with '' and everything before a comma only if ' (Observed)' is matched. Output should be:

1  "Independence Day"
2  "Christmas Day"
3  "New Year's Day"
4  "Martin Luther King, Jr. Day"

I was able to do both independently:

(foo['holiday']
 .replace(to_replace=' \(Observed\)', value='', regex=True)
 .replace(to_replace='.+, ', value='', regex=True))

but that caused a problem with 'Martin Luther King, Jr. Day'.

Answer 1

replace.py

import re

input = [
    "Independence Day (Observed)",
    "Christmas Eve, Christmas Day (Observed)",
    "New Year's Eve, New Year's Day (Observed)",
    "Martin Luther King, Jr. Day"
]

for holiday in input:
    print re.sub('^(.*?, )?(.*?)( \(Observed\))$', '\\2', holiday)

Output

> python replace.py 
Independence Day
Christmas Day
New Year's Day
Martin Luther King, Jr. Day

Explanation

• ^: Match at start of string.
• (.*?, )?: Match anything followed by a command and a space. Make it a lazy match, so it doesn't consume the portion of the string we want to keep. The last ? makes the whole thing optional, because some of the sample input doesn't have a comma at all.
• (.*?): Grab the part we want for later use in a capturing group. This part is also a lazy match because...
• ( \(Observed\)): Some strings might have " (Observed)" on the end, so we declare that in a separate group here. The lazy match in the prior piece won't consume this.
• $: Match at end of string.

Answer 2

I suggest

r'^(?:.*,\s*)?\b([^,]+)\s+\(Observed\).*'

Replace with r'\1' backreference.

See the regex demo.

Pattern details:

• ^ - start of string
• (?:.*,\s*)? - an optional sequence of:
  • .*, - any 0+ chars other than line break chars as many as possible, up to the last occurrence of , on the line and then the ,
  • \s* - 0 or more whitespaces
• \b - a word boundary
• ([^,]+) - 1 or more chars other than ,
• \s+ - 1 or more whitespaces
• \(Observed\) - a literal substring (Observed)
• .* - any 0+ chars other than line break chars as many as possible up to the line end.