Why Do Go and Python Regular Expressions Produce Different Results?

Regular Expression Behavior in Different Languages: Go vs. Python

When attempting to use regular expressions in Go, developers may encounter unexpected behavior. For instance, consider the following code:

package main

import (
    "fmt"
    "regexp"
)

func main() {
    a := "parameter=0xFF"
    regex := "^.+=\b0x[A-F][A-F]\b$"
    result, err := regexp.MatchString(regex, a)
    fmt.Println(result, err) // Prints: false <nil>
}

This code fails to match the expected input string, despite working correctly in Python:

import re

p = re.compile(r"^.+=\b0x[A-F][A-F]\b$")
m = p.match("parameter=0xFF")
if m is not None:
    print(m.group())  # Prints: parameter=0xFF

The root cause of this discrepancy lies in the differences between string literals in Go and Python. In Go, string literals are considered "cooked" by default, meaning they are interpreted for special characters like escape sequences. However, for regular expressions, this behavior is problematic.

To address this issue, Go provides raw string literals. Raw string literals are enclosed in back quotes (`) instead of quotes ("). They ignore any special characters or escape sequences, ensuring that the literal is interpreted exactly as written.

Therefore, to resolve the issue with the Go code, the regular expression should be specified as a raw string literal:

var regex = `^.+=\b0x[A-F][A-F]\b$`

With this modification, the code will now correctly match the input string and produce the desired result.

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