CODEWITHSUNDEEP
pythonpython-3.x
Erran Morad
Erran Morad

Reputation: 4753

Understanding file locations in python - unexpected errors

I am learning python 3.3 in windows 7. I have a two text files - lines.txt and raven.txt in a folder. Both contain the same text for the first example.

When I try to access ravens, using the code below, I get the error - 

OSError: [Errno 22] Invalid argument: 'C:\\Python\raven.txt'

I know that the above error can be fixed by using an escape character like this - 

C:\\Python\\raven.txt
C:\Python\\raven.txt

Why do both methods work ? Strangely, when I access lines.txt in the same folder, I get no error ! Why ?

import re

def main():
    print('')
    fh = open('C:\Python\lines.txt')

    for line in fh:
        if re.search('(Len|Neverm)ore', line):
            print(line, end = '')

if __name__ == '__main__':main()

Also, when I use the line below, I get a completely different error - TypeError: embedded NUL character. Why ?

fh = open('C:\Python\Exercise Files\09 Regexes\raven.txt')

I can rectify this by using \ before every \ in the file path.

Upvotes: 1

Views: 1516

Answers (3)

Alisa D.
Alisa D.

Reputation: 134

You can actually use forward slashes instead of backward ones, that way you don't have to escape them at all, which would save you a lot of headaches. Like this: 'C:/Python/raven.txt', I can guarantee that it works on Windows.

Upvotes: 1

Taha Jahangir
Taha Jahangir

Reputation: 4902

\r is an escape character, but \l is not. So, lines is interpreted as lines while raven is interpreted as aven, since \r is escaped.

In [1]: len('\l')
Out[1]: 2
In [2]: len('\r')
Out[2]: 1

You should always escape backslashes with \\. In cases your string doesn't have quotes, you can also use raw strings:

In [9]: len(r'\r')
Out[9]: 2
In [10]: r'\r'
Out[10]: '\\r'

See: https://docs.python.org/3/reference/lexical_analysis.html

Upvotes: 2

BlackMamba
BlackMamba

Reputation: 10252

maybe you can use raw string.

just like this open(r'C:\Python\Exercise Files\09 Regexes\raven.txt').

When an r' orR' prefix is present, backslashes are still used to quote the following character, but all backslashes are left in the string. For example, the string literal r"\n" consists of two characters: a backslash and a lowercase `n'. String quotes can be escaped with a backslash, but the backslash remains in the string; for example, r"\"" is a valid string literal consisting of two characters: a backslash and a double quote; r"\" is not a value string literal (even a raw string cannot end in an odd number of backslashes). Specifically, a raw string cannot end in a single backslash (since the backslash would escape the following quote character). Note also that a single backslash followed by a newline is interpreted as those two characters as part of the string, not as a line continuation.

Upvotes: 1

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