wcfg 4

Parser for hyerarchical text data and configuration files

wcfg is a small module to parse hierarchical data from text files, and it is particularly suitable for configuration files.

Features:

• Text-based, hierarchical format, with simple syntax which is designed to be easy to parse both by programs and humans.

• Both reading and writing back is supported. Written data is guaranteed to be readable back to its original representation.

• Small, self-contained, pure Python implementation.

• Compatible with both Python 2.6 and 3.2 (or newer).

Example

Given the following input file:

# Configuration file for SuperFooBar v3000
interface {
  language: "en_US"
  panes {
    top: ["menu", "toolbar"]  # Optional commas in lists
    # The colon separating keys and values is optional
    bottom
      ["statusbar"]
  }
  ☺ : True  # Enables emoji
  Unicode→Suþþorteð? : "Indeed, Jürgen!"
}

# Configure plug-ins
plugin: {
  preview  # Whitespace is mostly ignored
  {
    enabled: true
    timeout: 500  # Update every 500ms
  }
}

Note that the : separator in between keys and values is optional, and can be omitted. Also, notice how white space —including new lines— are completely meaningless and the structure is determined using only braces and brackets. Last but not least, a valid key is any Unicode character sequence which does not include white space or a colon.

The following code can be used to read it into a Python dictionary:

import wcfg
with open("superfoobar3000.conf", "rb") as f:
  config = wcfg.load(f)

Conversions work as expected:

• Sections are converted into dictionaries.

• Keys are converted conveted to strings.

• Text in double quotes are converted to strings.

• Sections enclosed into { } are converted to dictionaries.

• Arrays enclosed into [ ] are converted to lists.

• Numbers are converted either to int or float, whichever is more appropriate.

• Boolean values are converted to bool.

The following can be used to convert a Python dictionary into its textual representation:

users = {
  "peter": {
    "uid": 1000,
    "name": "Peter Jøglund",
    "groups": ["wheel", "peter"],
  },
  "root": {
    "uid": 0,
    "groups": ["root"],
  }
}

import wcfg
text = wcfg.dumps(users)

When generating a textual representation, the keys of each dictionary will be sorted, to guarantee that the generated output is stable. The dictionary from the previous snippet would be written in text form as follows:

peter: {
  name: "Peter Jøglund"
  groups: ["wheel" "peter"]
  uid: 1000
}
root: {
  groups: ["root"]
  uid: 0
}

Grammar

This is the grammar accepted by the parser, in EBNF syntax:

identifier = - ( whitespace | ":" )

string character = - "\""

key-value pair = identifier, ":", value
               | identifier, value

octal digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7"

digit = octal digit | "8" | "9"

hexdigit = digit | "a" | "b" | "c" | "d" | "e" | "f"
                 | "A" | "B" | "C" | "D" | "E" | "F"

sign = "-" | "+"

integral number = digit, { digit }

dotted float = ".", digit, { digit }
             | digit, ".", { digit }

exponent = ("e" | "E"), sign, digit, { digit }
         | ("e" | "E"), digit, { digit }

float number = dotted float
             | dotted float, exponent
             | integral number, exponent

number body = integral number
            | float number

number = "0", ( "x" | "X" ), hex digit, { hex digit }
       | "0", octal digit, { octal digit }
       | sign, number body
       | number body

boolean = "True" | "False"
        | "true" | "false"

value = "\"", { string character }, "\""
      | "[", { (value | value ",") } "]"
      | "{", { key-value pair }, "}"
      | boolean
      | number

input = "{", { key-value pair }, "}"
      | { key-value pair }

Note that comments are not specified in the grammar above does not include comments for the sake of simplicity. Comments can appear anywhere except inside strings, and they span from the octothorpe sign (#) to the end of the line.