What's the diff

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July 16th, 2012, 03:40 PM

WynnDeezl

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What's the diff

i have a text file resembling something like:

asfasdf
fkkfs
aghtj
sjsga
mwyha
kstjrjtjks
ehashah
adfgaa
eraaf

i read it in like this:

Code:

Lines = open('filename', 'r').readlines()
  for Line in Lines :
    if Line == 'mwyha' : print Line

i get no printed Line. however if i code it like this:

Code:

Lines = open('filename', 'r').readlines()
  for Line in Lines :
    if 'mwyha' in Line : print Line

i get Line showing up printed out...i don't understand why the first way doesn't work...any suggestions?

July 16th, 2012, 03:53 PM

sepp2k1

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The difference between "str1 == str2" and "str1 in str2" is that the former returns true if both strings are equal and the latter returns true if str1 is a substring of str2. So if str2 is "FOOhelloBAR" and str1 is "hello", then "str1 == str2" will obviously return false while "str1 in str2" will return true.

In your case the reason that the two strings are not equal is that readlines() does not strip off the newline character from the lines it reads, so Line will be equal to "mwyha\n" - not "mwyha".

July 16th, 2012, 03:56 PM

b49P23TIvg

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readlines() retains the end of line characters, on my system a linefeed. These are apparent if you have statements like:

print(len(Line),Line)
print(ord(Line[-1]))

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WynnDeezl agrees: Thank you!

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July 16th, 2012, 05:07 PM

Scorpions4ever

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Instead of using readlines, you can always now read from the file object directly.

Code:

file = open('filename', 'r')
for line in file:
    line = line.strip()
    if line == 'mywha': print line
file.close()

or if you want to compact it a bit:

Code:

for line in open('filename', 'r'):
    line = line.strip()
    if line == 'mywha': print line

In this case, the file will be automatically closed and garbage collected when it falls out of scope of the for loop.

Either of these two approaches is more memory-efficient than using readlines() because they don't read the entire file into memory ahead of time, just enough chunks to get the job done.

Comments on this post

WynnDeezl agrees: Thank you!

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