parse 1.1.8

Format Syntax

A basic version of the Format String Syntax is supported with anonymous (fixed-position), named and formatted fields:

{[field name]:[format spec]}

Field names must be a single Python identifier word. No attributes or element indexes are supported (as they would make no sense.)

Numbered fields are also not supported: the result of parsing will include the parsed fields in the order they are parsed.

The conversion of fields to types other than strings is done based on the type in the format specification, which mirrors the format() behaviour. There are no “!” field conversions like format() has.

Some simple parse() format string examples:

>>> parse("Bring me a {}", "Bring me a shrubbery")
<Result ('shrubbery',) {}>
>>> r = parse("The {} who say {}", "The knights who say Ni!")
>>> print r
<Result ('knights', 'Ni!') {}>
>>> print r.fixed
('knights', 'Ni!')
>>> r = parse("Bring out the holy {item}", "Bring out the holy hand grenade")
>>> print r
<Result () {'item': 'hand grenade'}>
>>> print r.named
{'item': 'hand grenade'}

Format Specification

Do remember that most often a straight format-less {} will suffice where a more complex format specification might have been used.

Most of the Format Specification Mini-Language is supported:

[[fill]align][sign][0][width][type]

The align operators will cause spaces (or specified fill character) to be stripped from the value. Similarly width is not enforced; it just indicates there may be whitespace or “0”s to strip.

The “#” format character is handled automatically by d, b, o and x - that is: if there is a “0b”, “0o” or “0x” prefix respectively, it’s handled. For “d” any will be accepted, but for the others the correct prefix must be present if at all.

The types supported are a slightly different mix to the format() types. Some format() types come directly over: d, n, %, f, e, b, o and x. In addition some regular expression character group types D, w, W, s and S are also available.

The “e” and “g” types are case-insensitive so there is not need for the “E” or “G” types.

So, for example, some typed parsing, and None resulting if the typing does not match:

>>> parse('Our {:d} {:w} are...', 'Our 3 weapons are...')
<Result (3, 'weapons') {}>
>>> parse('Our {:d} {:w} are...', 'Our three weapons are...')
None

And messing about with alignment:

>>> parse('with {:>} herring', 'with     a herring')
<Result ('a',) {}>
>>> parse('spam {:^} spam', 'spam    lovely     spam')
<Result ('lovely',) {}>

Note that the “center” alignment does not test to make sure the value is actually centered. It just strips leading and trailing whitespace.

See also the unit tests at the end of the module for some more examples. Run the tests with “python -m parse”.

Some notes for the date and time types:

• the presence of the time part is optional (including ISO 8601, starting at the “T”). A full datetime object will always be returned; the time will be set to 00:00:00.

• except in ISO 8601 the day and month digits may be 0-padded

• the separator for the ta and tg formats may be “-” or “/”

• named months (abbreviations or full names) may be used in the ta and tg formats

• as per RFC 2822 the e-mail format may omit the day (and comma), and the seconds but nothing else

• hours greater than 12 will be happily accepted

• the AM/PM are optional, and if PM is found then 12 hours will be added to the datetime object’s hours amount - even if the hour is greater than 12 (for consistency.)

• except in ISO 8601 and e-mail format the timezone is optional

• when a seconds amount is present in the input fractions will be parsed

• named timezones are not handled yet

Note: attempting to match too many datetime fields in a single parse() will currently result in a resource allocation issue.

Result Objects

The result of a parse() operation is either None (no match) or a Result instance.

The Result instance has three attributes:

fixed

A tuple of the fixed-position, anonymous fields extracted from the input.

named

A dictionary of the named fields extracted from the input.

spans

A dictionary mapping the names and fixed position indices matched to a 2-tuple slice range of where the match occurred in the input. The span does not include any stripped padding (alignment or width).

Version history (in brief):

• 1.1.8 allow “d” fields to have number base “0x” etc. prefixes; fix up some field type interactions after stress-testing the parser; implement “%” type.

• 1.1.7 Python 3 compatibility tweaks (2.5 to 2.7 and 3.2 are supported).

• 1.1.6 add “e” and “g” field types; removed redundant “h” and “X”; removed need for explicit “#”.

• 1.1.5 accept textual dates in more places; Result now holds match span positions.

• 1.1.4 fixes to some int type conversion; implemented “=” alignment; added date/time parsing with a variety of formats handled.

• 1.1.3 type conversion is automatic based on specified field types. Also added “f” and “n” types.

• 1.1.2 refactored, added compile() and limited from parse import *

• 1.1.1 documentation improvements

• 1.1.0 implemented more of the Format Specification Mini-Language and removed the restriction on mixing fixed-position and named fields

• 1.0.0 initial release

This code is copyright 2011 eKit.com Inc (http://www.ekit.com/) See the end of the source file for the license of use.