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Question

I have a file in which I need for a pattern and I need to extract the values after the pattern and I should append it to a list.

Sample of file I am using:

Container:container_12345

asfacaasda:..........
sdaasdasda:............
dasdadaadada.....

jiasjafjsdf.............
sdfsdfsd..................

Container:container_23456

dasdafsadf....
dfsdfsaf.....
fsfsfsdf......

I have tried to extract the values present after the pattern "Container:" (ie) container_12345

My code:

List = []
pattern=re.compile("Container:")
fop=open(filename,"r")
for line in fop:
    for char in line:
        result=pattern.search(char)
        List.append(result.group(1))

print(List)

My Output:

List.append(result.group(1))
AttributeError: 'NoneType' object has no attribute 'group'

Output what I am expecting:

['container_12345','container_23456']  #Present in that list

Please explain me what I have done wrong. Thanks in advance!

Answer 1

Regular expressions are a useless complication if you are looking for a static string.

for line in lines:
    if line.startswith("Container:"):
        print(line[len("Container:"):].strip())

The call to strip() trims any whitespace from the beginning or the end; if you omit it, keep in mind that line ends with a newline character.

The actual error in your code is that you attempt to extract something even when search returns None ; also, your regex seems slightly wrong, and you needlessly iterate over each character in each line, so the regex will never match.

Answer 2

Just use the expression on the whole content instead of iterating over it line by line.
The re module has builtin functionality exactly fort his purpose:

import re
rx = re.compile('^Container:\s*(.+)', re.M)
with open(your_file) as fp:
    containers = [m.group(1) for m in rx.finditer(fp.read())]
    print(containers)