When working with date and time information in Python, you commonly use the
classes date, datetime and/or time from the datetime package.
Babel provides functions for locale-specific formatting of those objects in its
dates module:
System Message: ERROR/3 (doc/dates.txt, line 20)
Unknown directive type "code-block".
.. code-block:: pycon
>>> from datetime import date, datetime, time
>>> from babel.dates import format_date, format_datetime, format_time
>>> d = date(2007, 4, 1)
>>> format_date(d, locale='en')
u'Apr 1, 2007'
>>> format_date(d, locale='de_DE')
u'01.04.2007'
As this example demonstrates, Babel will automatically choose a date format
that is appropriate for the requested locale.
The format_*() functions also accept an optional format argument, which
allows you to choose between one of four format variations:
While Babel makes it simple to use the appropriate date/time format for a given
locale, you can also force it to use custom patterns. Note that Babel uses
different patterns for specifying number and date formats compared to the
Python equivalents (such as time.strftime()), which have mostly been
inherited from C and POSIX. The patterns used in Babel are based on the
Locale Data Markup Language specification (LDML), which defines them as
follows:
A date/time pattern is a string of characters, where specific strings of
characters are replaced with date and time data from a calendar when formatting
or used to generate data for a calendar when parsing. […]
Characters may be used multiple times. For example, if y is used for the
year, yy might produce "99", whereas yyyy produces "1999". For most
numerical fields, the number of characters specifies the field width. For
example, if h is the hour, h might produce "5", but hh produces
"05". For some characters, the count specifies whether an abbreviated or full
form should be used […]
Two single quotes represent a literal single quote, either inside or outside
single quotes. Text within single quotes is not interpreted in any way (except
for two adjacent single quotes).
The syntax for custom datetime format patterns is described in detail in the
the Locale Data Markup Language specification. The following table is just a
relatively brief overview.
1.1 Date Fields
Field
Symbol
Description
Era
G
Replaced with the era string for the current date. One
to three letters for the abbreviated form, four
lettersfor the long form, five for the narrow form
Year
y
Replaced by the year. Normally the length specifies
the padding, but for two letters it also specifies the
maximum length.
Y
Same as y but uses the ISO year-week calendar.
u
??
Quarter
Q
Use one or two for the numerical quarter, three for
the abbreviation, or four for the full name.
q
Use one or two for the numerical quarter, three for
the abbreviation, or four for the full name.
Month
M
Use one or two for the numerical month, three for the
abbreviation, or four for the full name, or five for
the narrow name.
L
Use one or two for the numerical month, three for the
abbreviation, or four for the full name, or 5 for the
narrow name.
Week
w
Week of year.
W
Week of month.
Day
d
Day of month.
D
Day of year.
F
Day of week in month.
g
??
Week day
E
Day of week. Use one through three letters for the
short day, or four for the full name, or five for the
narrow name.
e
Local day of week. Same as E except adds a numeric
value that will depend on the local starting day of
the week, using one or two letters.
c
??
1.2 Time Fields
Field
Symbol
Description
Period
a
AM or PM
Hour
h
Hour [1-12].
H
Hour [0-23].
K
Hour [0-11].
k
Hour [1-24].
Minute
m
Use one or two for zero places padding.
Second
s
Use one or two for zero places padding.
S
Fractional second, rounds to the count of letters.
A
Milliseconds in day.
Timezone
z
Use one to three letters for the short timezone or
four for the full name.
Z
Use one to three letters for RFC 822, four letters for
GMT format.
v
Use one letter for short wall (generic) time, four for
long wall time.
V
Same as z, except that timezone abbreviations
should be used regardless of whether they are in
common use by the locale.
2 Time-zone Support
Many of the verbose time formats include the time-zone, but time-zone
information is not by default available for the Python datetime and
time objects. The standard library includes only the abstract tzinfo
class, which you need appropriate implementations for to actually use in your
application. Babel includes a tzinfo implementation for UTC (Universal
Time).
For real time-zone support, it is strongly recommended that you use the
third-party package pytz, which includes the definitions of practically all
of the time-zones used on the world, as well as important functions for
reliably converting from UTC to local time, and vice versa:
System Message: ERROR/3 (doc/dates.txt, line 215)
Unknown directive type "code-block".
.. code-block:: pycon
>>> from datetime import time
>>> from pytz import timezone, utc
>>> dt = datetime(2007, 04, 01, 15, 30, tzinfo=utc)
>>> eastern = timezone('US/Eastern')
>>> format_datetime(dt, 'H:mm Z', tzinfo=eastern, locale='en_US')
u'11:30 -0400'
The recommended approach to deal with different time-zones in a Python
application is to always use UTC internally, and only convert from/to the users
time-zone when accepting user input and displaying date/time data, respectively.
You can use Babel together with pytz to apply a time-zone to any
datetime or time object for display, leaving the original information
unchanged:
System Message: ERROR/3 (doc/dates.txt, line 231)
Unknown directive type "code-block".
.. code-block:: pycon
>>> british = timezone('Europe/London')
>>> format_datetime(dt, 'H:mm zzzz', tzinfo=british, locale='en_US')
u'16:30 British Summer Time'
Here, the given UTC time is adjusted to the "Europe/London" time-zone, and
daylight savings time is taken into account. Daylight savings time is also
applied to format_time, but because the actual date is unknown in that
case, the current day is assumed to determine whether DST or standard time
should be used.
2.1 Localized Time-zone Names
While the Locale class provides access to various locale display names
related to time-zones, the process of building a localized name of a time-zone
is actually quite complicated. Babel implements it in separately usable
functions in the babel.dates module, most importantly the
get_timezone_name function:
System Message: ERROR/3 (doc/dates.txt, line 255)
Unknown directive type "code-block".
.. code-block:: pycon
>>> from pytz import timezone
>>> from babel import Locale
>>> from babel.dates import get_timezone_name
>>> tz = timezone('Europe/Berlin')
>>> get_timezone_name(tz, locale=Locale.parse('pt_PT'))
u'Hor\xe1rio Alemanha'
You can pass the function either a datetime.tzinfo object, or a
datetime.date or datetime.datetime object. If you pass an actual date,
the function will be able to take daylight savings time into account. If you
pass just the time-zone, Babel does not know whether daylight savings time is
in effect, so it uses a generic representation, which is useful for example to
display a list of time-zones to the user.