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Handle Windows paths in Python

Handle Windows paths in Python

David Y.

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The Problem

I’m getting a strange error when attempting to open a file with Python on Windows. Here’s my code:

Click to Copy
import csv

data = open("C:\Users\sam\Documents\data\1.5\data.csv")
data = csv.reader(data)
print(data)

When I try to execute it, I get this error:

Click to Copy
SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes in position 2-3: truncated \UXXXXXXXX escape

The Solution

The error is caused by the backslash character (\) that is used by Python for escape sequences to represent special characters, for example, \n for new line. The error message indicates that Python is attempting to interpret the \User section of the path string as a Unicode code point because it starts with \U.

We can get around this in a few different ways.

Use Raw Strings

By placing an r in front of a string, we instruct Python not to look for escape sequences within it, and thus force it to treat any backslashes as literal backslashes.

Click to Copy
import csv

data = open(r"C:\Users\sam\Documents\data\1.5\data.csv")
data = csv.reader(data)
print(data)

Use Forward Slashes

File paths on Mac and *nix-based systems use forward slashes rather than backslashes to denote folder structure. Python allows us to do this on Windows as well:

Click to Copy
import csv

data = open("C:/Users/sam/Documents/data/1.5/data.csv")
data = csv.reader(data)
print(data)

This approach has the advantage of making partial or relative path strings work across platforms. For example, the path sam/Documents/data/1.5/data.csv could be resolved to /home/sam/Documents/data/1.5/data.csv on a Linux system or C:\Users\sam\Documents\data\1.5\data.csv on a Windows system, as long as the script is executed in /home/ or C:\Users.

Use Double Backslashes

In a standard Python string, the escape sequence \\ translates to \. Therefore, a third way we can resolve this problem is by replacing all \s with \\s in the path.

Click to Copy
import csv

data = open("C:\\Users\\sam\\Documents\\data\\1.5\\data.csv")
data = csv.reader(data)
print(data)
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