How can I read blackslashes from a file correctly?

The following code:

key = open("C:\Scripts\private.ppk",'rb').read()

reads the file and assigns its data to the var key.

For a reason, backslashes are multiplied in the process. How can I make sure 开发者_开发技巧they don't get multiplied?

You ... don't. They are escaped when they are read in so that they will process properly when they are written out / used. If you're declaring strings and don't want to double up the back slashes you can use raw strings r'c:\myfile.txt', but that doesn't really apply to the contents of a file you're reading in.

>>> s = r'c:\boot.ini'
>>> s
'c:\\boot.ini'
>>> repr(s)
"'c:\\\\boot.ini'"
>>> print s
c:\boot.ini
>>>

As you can see, the extra slashes are stored internally, but when you use the value in a print statement (write a file, test for values, etc.) they're evaluated properly.

You should read this great blog post on python and the backslash escape character.

And under some circumstances, if Python prints information to the console, you will see the two backslashes rather than one. For example, this is part of the difference between the repr() function and the str() function.

myFilename = "c:\newproject\typenames.txt" print repr(myFilename), str(myFilename) produces

'c:\newproject\typenames.txt' c:\newproject\typenames.txt

Backslashes are represented as escaped. You'll see two backslashes for each real one existing on the file, but that is normal behaviour.

The reason is that the backslash is used in order to create codes that represent characters that cannot be easily represented, such as new line '\n' or tab '\t'.

Are you trying to put single backslashes in a string? Strings with backslashes require and escape character, in this case "\". It will print to the screen with a single slash

In fact there is a solution - using eval, as long as the file content can be wrapped into quotes of some kind. Following worked for me (PATH contains some script that executes Matlab):

MATLAB_EXE = "C:\Program Files (x86)\MATLAB\R2012b\bin\matlab.exe"
content = open(PATH).read()
MATLAB_EXE in content  # False
content = eval(f'r"""{content}"""')
MATLAB_EXE in content  # True

This works by evaluating the content as python string literal, making double escapes transform into single ones. Raw string is used to prevent escapes forming special characters.