How To Write Correct Regex Format For Finding And Replacing Lines In A File

I have got two files, and both of them looks like (Except the data after K in each line starting only with PBUSH in both the files ) : $ Elements and Element Properties for reg

Solution 1:

In general case one would parse and write the BDF files with something like the pyNastran.

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However in this specific case using your approach is not that wrong; though your regular expressions are wrong, though the principle works here. Notice also, you need to use raw strings or escape \ in the paths; the use of unescaped \ is being deprecated and can lead to hard-to-find errors.

import re

# must use raw strings for paths, otherwise we need to# escape \ characters
input1 = r"C:\Users\sony\Desktop\PBUSH1.BDF"
input2 = r"C:\Users\sony\Desktop\PBUSH2.BDF"

output = r"C:\Users\sony\Desktop\OUTPUT.BDF"withopen(path1) as f1, open(path2) as f2:
    dat1 = f1.read()
    dat2 = f2.read()

# use finditer instead of findall so that we will get # a match object for each match.## For each matching line we also have one subgroup, containing the# "PBUSH   NNN     " part, whereas the whole regex matches until# the next end of line
matches = re.finditer('^(PBUSH\s+[0-9]+\s+).*$', dat1, flags=re.MULTILINE)

for match in matches:
    # for each match we construct a regex that looks like# "^PBUSH   123      .*$", then replace all matches thereof# with the contents of the whole line
    dat2 = re.sub('^{}.*$'.format(match.group(1)), match.group(0), dat2, flags=re.MULTILINE)

withopen(output) as outf:
    outf.write(dat2)