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String.find () always evaluates to true

I have a small script that reads a file. After reading the line, I'm trying to figure out that the particular line has special text in it. For this I like this

for line in file:
    line = line.lower()

    if line.find('my string'):
        print ('found my string in the file')

reading a file that line.find always evaluates to true. When i like

for line in file:
    line = line.lower()

    if 'one big line'.find('my string'):
        print ('found my string in the file')

It evaluates to false as expected. Since I'm really new to python programming just for what I've shown, I just can't think of what I can find ...

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2 answers


Better idiomatic python to write it like:

for line in file:
    line = line.lower()

    if 'my string' in line:
        print ('found my string in the file')


instead of using .find()

it if you don't want the position within the string.

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find

returns the number containing the occurring string within the search string. If it doesn't find it, it returns -1

. And every number that is not 0

in python evaluates to True

. This is why your code is always evaluating True

.

You need something like:

if 'one big line'.find('my string') >= 0:
    print ('found my string in the file')


Or, better:

idx = 'one big line'.find('my string')
if idx >= 0:
    print ("found 'my string' in position %d" % (idx))
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