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Pattern matching dispute in Python 3.10

Seeking Patterns

Article from ADMIN 63/2021

By Veit Schiele

A controversial change is taking place in Python version 3.10 known mainly from functional languages: pattern matching.

Pattern matching is a symbol processing technique that uses a pattern to identify discrete structures or subsets, such as strings, trees, or graphs. It is found in functional or logic programming languages that use a match expression to process data on the basis of its structure (e.g., in Scala [1], Rust [2], and F# [3]). A match statement takes an expression and compares it with successive patterns, which the programmer specifies in terms of one or more cases. This method is superficially similar to a switch statement in C, Java, or JavaScript, but far more powerful.

Python 3.10 is now also set to receive such a match expression. The Python enhancement proposal (PEP) 634 [4] describes the implementation. More information about the plans can be found in PEP 635 [5] and PEP 636 [6]. How pattern matching is intended to work in Python 3.10 is demonstrated by the simple example in Listing 1, which compares a value with multiple literals.

Listing 1

Intended Pattern Matching

def http_error(status):
      match status:
          case 400:
              return "Bad request"
          case 401:
              return "Unauthorized"
          case 403:
              return "Forbidden"
          case 404:
              return "Not found"
          case 418:
              return "I'm a teapot"
          case _:
              return "Something

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