How to replace string in original file with string from new file in Python

Question

I have an original config file that has a string:

boothNumber="5"

In my program, I grab a similar config from another computer. This similar config has a string:

boothNumber="1"

I want to read the new number which is 1 and replace the original config with the number 1(replaces 5).

I am getting an error in my program that says:

TypeError: coercing to str: need a bytes-like object, NoneType found

Any ideas?

import os
import shutil
import fileinput
import pypyodbc
import re                                     # used to replace string
import sys                                    # prevents extra lines being inputed in config


def readconfig(servername):
    destsource = 'remote.config'                                            # file that I grabbed from remote computer
    template = 'original.config'                                        # original config
    for line in open(destsource):                                       # open new config
        match = re.search(r'(?<=boothNumber=")\d+', line)               #find a number after a certain string and name it 'match'

        with fileinput.FileInput(template, inplace=True, backup='.bak') as file:  # open original config
            for f2line in file:
                pattern = r'(?<=boothNumber=")\d+'                      # find number after certain string and name it 'pattern'


                if re.search(pattern, f2line):                          # if line has 'pattern'
                    sys.stdout.write(re.sub(pattern, match, f2line))    # replace 'pattern' number with number from 'match'
                    fileinput.close()



def copyfrom(servername):
    # copy config from server


    source = r'//' + servername + '/c$/configdirectory'
    dest = r"C:/myprogramdir"
    file = "remote.config"
    try:
        shutil.copyfile(os.path.join(source, file), os.path.join(dest, file))
        # you can't just use shutil when copying from a remote computer.  you have to also use os.path.join
    except:
        copyerror()

    readconfig(servername)



os.system('cls' if os.name == 'nt' else 'clear')
array = []
with open("serverlist.txt", "r") as f:       # list of computer names
    for servername in f:

        copyfrom(servername.strip())

Could you post the whole traceback?

elena
– elena

2017-06-03 05:40:13 +00:00
Commented Jun 3, 2017 at 5:40 — elena
– elena, Commented Jun 3, 2017 at 5:40

snakecharmerb · Accepted Answer · 2017-06-10 11:47:19Z

In your readConfig function, this line performs a search:

match = re.search(r'(?<=boothNumber=")\d+', line)

and the value of match is used in this line:

sys.stdout.write(re.sub(pattern, match, f2line))

There are two problems here. Firstly, if the search is unsuccessful match will be None, causing to the exception that you report:

 >>> re.sub(r'[a-z]+', None, 'spam')
Traceback (most recent call last):
...
TypeError: decoding to str: need a bytes-like object, NoneType found

Secondly, if match is not None, you are trying to use match itself as replacement string, but match is not a string, it's a match object:

>>> match = re.search(r'[a-z]+', 'spam')
>>> match
<_sre.SRE_Match object; span=(0, 4), match='spam'>  # <=== not a string!
>>> re.sub(r'[a-z]+', match, 'eggs')
Traceback (most recent call last):
  ...
TypeError: decoding to str: need a bytes-like object, _sre.SRE_Match found

You need to call match.group() to get the string that has been matched:

>>> re.sub(r'[a-z]+', match.group(), 'eggs')
'spam'

To summarise:

condition the output processing on match not being None
use match.group() as the replacement string

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