如何用“||”替换第一个和最后一个“,”分隔符来自 csv 而其他人保持原样？

Question

I have a CSV file:

101, "Name1", "Designation1", "blah1", "Blah1", 20200914001
102, "Name2", "Designation2", "blah2", "Blah2", 20200914002
103, "Name3", "Designation3", "blah3", "Blah3", 20200914003
104, "Name4", "Designation4", "blah4", "Blah4", 20200914004
105, "Name5", "Designation5", "blah5", "Blah5", 20200914005

replace each line like below:

101|| "Name1", "Designation1", "blah1", "Blah1"|| 20200914001

similar structure goes to the rest of the lines/records as well.

My code replaces all of the delimiters.

data = ""
with open('firstCSV.csv', 'r') as file:
    data = file.read().replace(',', '||').replace(' ', '')

with open("first_Out.csv", "w") as out_file:
    out_file.write(data)

Thanks in advance.

Answer 1

Use

^([^,]*),|,(?=[^,]*$)

Replace with \\1|| . See proof .

Explanation

--------------------------------------------------------------------------------
  ^                        the beginning of the string
--------------------------------------------------------------------------------
  (                        group and capture to \1:
--------------------------------------------------------------------------------
    [^,]*                    any character except: ',' (0 or more
                             times (matching the most amount
                             possible))
--------------------------------------------------------------------------------
  )                        end of \1
--------------------------------------------------------------------------------
  ,                        ','
--------------------------------------------------------------------------------
 |                        OR
--------------------------------------------------------------------------------
  ,                        ','
--------------------------------------------------------------------------------
  (?=                      look ahead to see if there is:
--------------------------------------------------------------------------------
    [^,]*                    any character except: ',' (0 or more
                             times (matching the most amount
                             possible))
--------------------------------------------------------------------------------
    $                        before an optional \n, and the end of
                             the string
--------------------------------------------------------------------------------
  )                        end of look-ahead

Python code :

import re

regex = r'^([^,]*),|,(?=[^,]*$)'
test_str = r'101, "Name1", "Designation1", "blah1", "Blah1", 20200914001'
subst = r'\1||'
print(re.sub(regex, subst, test_str))

Result: 101|| "Name1", "Designation1", "blah1", "Blah1"|| 20200914001 101|| "Name1", "Designation1", "blah1", "Blah1"|| 20200914001 101|| "Name1", "Designation1", "blah1", "Blah1"|| 20200914001 .

Answer 2

You could split on the first ( maxsplit=1 from the left) and last ( maxsplit=1 from the right) commas and join the results, eg:

>>> line = '101, "Name1", "Designation1", "blah1", "Blah1", 20200914001'

>>> first, rest = line.split(',', maxsplit=1)
>>> rest, last = rest.rsplit(',', maxsplit=1)
>>> '||'.join((first, rest, last))
'101|| "Name1", "Designation1", "blah1", "Blah1"|| 20200914001'