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How to Resolve Python Error "SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes"

Encountering a SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes in position X-Y: truncated \UXXXXXXXX escape in Python usually happens when working with string literals, especially those representing file paths on Windows. This error signals an issue with how Python interprets backslash (\) characters within the string.

This guide explains the cause of this specific Unicode decoding error and provides the standard solutions to fix it.

Understanding the Error: Backslashes and Escape Sequences​

In standard Python string literals (those enclosed in single ' or double " quotes), the backslash (\) character acts as an escape character. It signifies that the character(s) immediately following it have a special meaning:

  • \n: Newline
  • \t: Horizontal Tab
  • \\: Literal backslash
  • \': Literal single quote
  • \": Literal double quote
  • \uXXXX: Unicode character with the 16-bit hex value XXXX
  • \UXXXXXXXX: Unicode character with the 32-bit hex value XXXXXXXX

The unicodeescape codec is responsible for interpreting these \u and \U escape sequences.

The Common Cause: Unescaped Backslashes in Windows Paths​

Windows uses backslashes (\) as path separators (e.g., C:\Users\YourName). When you put such a path directly into a standard Python string literal, Python tries to interpret sequences starting with \ as escape sequences.

The specific error message truncated \UXXXXXXXX escape occurs most often when Python encounters \U within the path (like in C:\Users\...). Python sees \U and expects exactly eight hexadecimal characters immediately following it to represent a 32-bit Unicode character. Since the characters s, e, r, s are not hexadecimal digits, the unicodeescape codec fails to decode the sequence, resulting in the SyntaxError.

# Example causing the error
windows_path = 'C:\Users\Tom\Desktop\file.txt' # Problem: \U is followed by 's'

try:
    # ⛔️ File "...", line X
    #     windows_path = 'C:\Users\Tom\Desktop\file.txt'
    #                                                  ^
    # SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes
    #              in position 2-3: truncated \UXXXXXXXX escape
    print(f"Trying to use path: {windows_path}")
    # with open(windows_path, 'r') as f: ...
except SyntaxError as e:
    print(f"Caught SyntaxError:\n{e}")
note

Other sequences like \t in C:\tmp might also be interpreted unintentionally, though \U is a common trigger for this specific SyntaxError.

Prefixing the string literal with r (or R) creates a raw string. In a raw string, backslashes lose their special escape sequence meaning and are treated as literal backslash characters. This is the most common and recommended way to handle Windows paths in Python.

# ✅ Solution: Use a raw string by prefixing with 'r'
file_path_raw = r'C:\Users\Tom\Desktop\file.txt'

print(f"Path using raw string: {file_path_raw}")
# Output: Path using raw string: C:\Users\Tom\Desktop\file.txt

# Now you can use it safely with file operations
try:
    # Assuming the file exists for demonstration
    # with open(file_path_raw, 'r', encoding='utf-8') as f:
    #     print("File opened successfully (using raw string).")
    pass # Placeholder for file operation
    print("Path string is now valid.")
except FileNotFoundError:
    print(f"File not found at: {file_path_raw}")
except Exception as e:
    print(f"An error occurred: {e}")

# Triple-quoted raw strings also work (r'''...''' or r"""...""")
# Useful for multi-line raw strings, but overkill for simple paths.
file_path_raw_triple = r'''C:\Users\Tom\Desktop\file.txt'''
print(f"Path using triple-quoted raw string: {file_path_raw_triple}")

Solution 2: Use Forward Slashes (/) (Cross-Platform)​

Python, even on Windows, generally understands forward slashes (/) as path separators in functions like open(). Replacing backslashes with forward slashes avoids the escape sequence issue entirely and makes your path strings more portable across operating systems (Linux, macOS, Windows).

# ✅ Solution: Use forward slashes
file_path_forward = 'C:/Users/Tom/Desktop/file.txt'

print(f"Path using forward slashes: {file_path_forward}")
# Output: Path using forward slashes: C:/Users/Tom/Desktop/file.txt

# This path can typically be used directly in file operations
try:
    # with open(file_path_forward, 'r', encoding='utf-8') as f:
    #     print("File opened successfully (using forward slashes).")
    pass
    print("Path string is now valid.")
except FileNotFoundError:
    print(f"File not found at: {file_path_forward}")
except Exception as e:
    print(f"An error occurred: {e}")

This is often the preferred method if cross-platform compatibility is a goal.

Solution 3: Escape Each Backslash (\\)​

You can manually escape each backslash by preceding it with another backslash (\\). This tells Python to treat the second backslash as a literal character.

# ✅ Solution: Escape each backslash manually
file_path_escaped = 'C:\\Users\\Tom\\Desktop\\file.txt'

print(f"Path using escaped backslashes: {file_path_escaped}")
# Output: Path using escaped backslashes: C:\Users\Tom\Desktop\file.txt

# This path can also be used in file operations
try:
    # with open(file_path_escaped, 'r', encoding='utf-8') as f:
    #     print("File opened successfully (using escaped backslashes).")
    pass
    print("Path string is now valid.")
except FileNotFoundError:
    print(f"File not found at: {file_path_escaped}")
except Exception as e:
    print(f"An error occurred: {e}")

While this works, it makes path strings less readable and more tedious to type compared to raw strings or forward slashes.

Why \U Specifically Causes the Error​

The error message truncated \UXXXXXXXX escape is specific because \U starts a 32-bit Unicode escape sequence. Python requires exactly 8 hexadecimal digits (0-9, a-f, A-F) after \U. When it sees \Users, the s is not a valid hexadecimal digit, and there aren't 8 characters anyway. The unicodeescape codec cannot complete the decoding process, leading to the SyntaxError. Other invalid escape sequences might raise different syntax errors, but this one is characteristic of unescaped \U in paths.

Choosing the Best Solution for Paths​

  • Raw Strings (r'...'): Excellent for Windows paths containing backslashes when you want the string to exactly represent the path as written. Simple and clear.
  • Forward Slashes ('...'): Often the best choice for cross-platform compatibility. Python handles them correctly on Windows for most file operations. Makes code potentially runnable on Linux/macOS without path modification.
  • Escaping (\\): Least preferred for paths due to poor readability and ease of making mistakes.

Conclusion​

The SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes... truncated \UXXXXXXXX escape occurs when Python encounters an unescaped backslash (\) in a standard string literal, particularly the sequence \U followed by non-hexadecimal characters, as often happens in Windows file paths. To resolve this:

  1. Use raw strings by prefixing the literal with r (e.g., r'C:\Users\...'). This treats backslashes literally. (Recommended for Windows-specific paths)
  2. Use forward slashes (/) as path separators (e.g., 'C:/Users/...'). This works on Windows and improves cross-platform compatibility. (Often preferred)
  3. Manually escape each backslash with another backslash (\\) (e.g., 'C:\\Users\\...'). (Less readable)

By correctly handling backslashes in your string literals, especially file paths, you can easily avoid this common syntax error.

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