Question

Suppose I have a text file where each line contains either ‘1’ or ‘-1.’ How do I search through the file to check if the file contains at least one ‘1’?

Initially, I had the following.

if re.search(r'\b1', f.read()): return true
else: return false

However, this does not work because ‘-‘ is not considered an alphanumeric string and returns true if the file does not contain a single ‘1.’ What is the best way to determine if the file contains ‘1’?

Answer 1

Using the re.MULTILINE flag, ^ will match start of lines (instead of only start of subject):

re.search(re.compile('^1', re.MULTILINE), f.read())

This will match if any line starts with 1.

See http://docs.python.org/library/re.html#regular-expression-syntax

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This alternative solution avoid reading the file entirely:

has_1 = any(line == "1" for line in f)