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What exactly do 'u' and 'r' string flags do, and what are raw string literals in Python?

By IncludeHelp Last updated : December 08, 2024

Prefix of 'u' with a string

The prefix of 'u' in a string denotes the value of type Unicode rather than string (str). However, the Unicode strings are no longer used in Python3. The prefix of 'u' in a string denotes the value of type Unicode rather than str. However, the Unicode strings are no longer used in Python3. 

In Python2, if we type a string literal without 'u' in front, we get the old str type which stores 8-bit characters, and with 'u' in front we get the newer Unicode type that can store any Unicode character.

Prefix of 'r' with a string

Additionally adding 'r' doesn't change the type of the literal, just changes how the string literal is interpreted. Without the 'r' backlashes (/) are treated as escape characters. With 'r' (/) are treated as literal.

Raw strings

Prefixing the string with 'r' makes the string literal a 'raw string'. Python raw string treats backslash (\) as a literal character, which makes it useful when we want to have a string that contains backslash and don’t want it to be treated as an escape character.

Example 1

Consider the below example, where (\) has a special meaning.

s='Hi\nHello'
print(s)

r=r'Hi\nHello'
print(r)

Output

The output of the above example is:

Hi
Hello
Hi\nHello

Example 2

Consider the below example, where (\) doesn't have special meaning,

s='Hi\xHello'

Output

The output of the above example is:

  File "main.py", line 1
    s='Hi\xHello'
      ^
SyntaxError: (unicode error) 'unicodeescape' codec can't decode bytes in position 2-3: truncated \xXX escape

Example 3

s=r'Hi\xHello'
print(s)

Output

The output of the above example is:

Hi\xHello