Parse Expressions

Parse expressions are a simplified form of regular expressions. The actual regular expression is hidden behind the type name / hint.

Parse expressions are used in step definitions as a simplified alternative to regular expressions. They are used for parameters and type conversions (which are not supported for regular expression patterns).

# -- FILE: features/steps/example_steps.py
from behave import when

@when('we implement {number:d} tests')
def step_impl(context, number):  # -- NOTE: number is converted into integer
    assert number > 1 or number == 0
    context.tests_count = number

The following tables provide a overview of the parse expressions syntax. See also Python regular expressions description in the Python re module.

Type	Characters Matched	Output
l	Letters (ASCII)	str
w	Letters, numbers and underscore	str
W	Not letters, numbers and underscore	str
s	Whitespace	str
S	Non-whitespace	str
d	Digits (effectively integer numbers)	int
D	Non-digit	str
n	Numbers with thousands separators (, or .)	int
%	Percentage (converted to value/100.0)	float
f	Fixed-point numbers	float
F	Decimal numbers	Decimal
e	Floating-point numbers with exponent e.g. 1.1e-10, NAN (all case insensitive)	float
g	General number format (either d, f or e)	float
b	Binary numbers	int
o	Octal numbers	int
x	Hexadecimal numbers (lower and upper case)	int
ti	ISO 8601 format date/time e.g. 1972-01-20T10:21:36Z (“T” and “Z” optional)	datetime
te	RFC2822 e-mail format date/time e.g. Mon, 20 Jan 1972 10:21:36 +1000	datetime
tg	Global (day/month) format date/time e.g. 20/1/1972 10:21:36 AM +1:00	datetime
ta	US (month/day) format date/time e.g. 1/20/1972 10:21:36 PM +10:30	datetime
tc	ctime() format date/time e.g. Sun Sep 16 01:03:52 1973	datetime
th	HTTP log format date/time e.g. 21/Nov/2011:00:07:11 +0000	datetime
ts	Linux system log format date/time e.g. Nov 9 03:37:44	datetime
tt	Time e.g. 10:21:36 PM -5:30	time

If parse_type module is used, the cardinality of a type can be specified, too (by using the CardinalityField support):

Cardinality	Description
?	Pattern with cardinality 0..1: optional part (question mark).
*	Pattern with cardinality zero or more, 0.. (asterisk).
+	Pattern with cardinality one or more, 1.. (plus sign).