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INI Configuration File Parsing Task

This task parses a specific subset of the INI file format. For example:

[Colors]
; colors are 3-digit hex RGB values
red=#f00
green=#0f0
blue=#00f

INI files are notoriously ill-defined, particularly for corner cases, but generally follow some basic principles:

  • Keys are separated from values with some delimiter
  • Key-value pairs are grouped in sections
  • Sections are indicated with square brackets (e.g., [Section Name])
  • Line comments are prefixed with a special character

In order to make this task comparable to (a subset of) the Python standard library's configparser module, the following additional constraints are added:

  • Keys without values or delimiters are allowed (value is None)
  • Keys with a delimiter but without a value are allowed (value is '')
  • Sections and keys may be indented
  • Whitespace around keys and values is stripped
  • Whitespace within keys and values is not normalized
  • Only the = character is used as a key-value delimiter
  • Only the ; character is used to start comments
  • Comments are whole-line only (cannot appear on the same line as a section header, key, or value)
  • Values may not span multiple lines
  • There are no escaped characters
  • There is no interpolation of values
  • There is no default section
  • The parser should return a standard dict object.

Here is a illustrative PEG:

Start   <- Section* Comment* EOF
Section <- Comment* Header Body
Header  <- Space* Title Space* (EOL / EOF)
Title   <- '[' (![\]=\n\r] .)* ']'
Body    <- (Comment* Pair)*
Pair    <- Space* Key ('=' Value)?
Key     <- !Title (![=\n\r] .)*
Value   <- (!EOL .)*

Comment <- Space* (';' (!EOL .)*)? (EOL / EOF)
Space   <- [\t ]
EOL     <- '\r\n' / [\n\r]
EOF     <- !.

Extras

In future iterations of this task consider the following extensions.

Multiline Values

It would be nice to accommodate multi-lined values. Python's configparser uses indentation for this, e.g.:

[Poems]
roses are red=
  These key-value pairs,
  Grouped into a section,
  Mathematically speaking,
  Are like a surjection.

Other parsers may escape newlines or use some other technique. The indentation one is perhaps more challenging to parse than other techniques.

Extra: Simple Validation

  • Duplicate keys within a section raise an error
  • Duplicate section names raise an error