python & django timezone usage

In production, there are multiple time zones, users are more likely to stay in different time zones, if the website is desgined for users in multiple time zones and only use standard time, there will be a deviation in calculation.

To solve the problems like this, using the UTC stanard time in code and database, and it is a good choice to use local time only when interacting with front end users.

Django disabled time zone support by default, you can set USE_TZ = True to enable time zone support in settings. It is best to install the pytz module (pip install pytz) at the same time.

Python datetime.datetime object has a attribute called tzinfo, it’s used for storing timezone infos. You can use is_aware() and is_naive() methods to check what kind of datetime object is. django.utils.timezone.is_aware()

Using django native datetime object to store local time when django timezone disabled:

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import datetime
now = datetime.datetime.now()  

Using django aware datetime object to store local time when django timezone enabled:

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from django.utils import timezone
now = timezone.now()  # datetime.datetime(2019, 6, 17, 8, 36, 22, 292901, tzinfo=<UTC>)

1. Django Timezone

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from django.utils import timezone
now = timezone.now()  # datetime.datetime(2019, 6, 17, 8, 36, 22, 292901, tzinfo=<UTC>)
new = timezone.localtime(now)  # datetime.datetime(2019, 6, 17, 16, 36, 22, 292901, tzinfo=<DstTzInfo 'Asia/Shanghai' CST+8:00:00 STD>)

2. Python Timezone

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import datetime
import pytz
now = datetime.datetime.now()  # datetime.datetime(2019, 6, 17, 16, 39, 5, 65823)
new = now.replace(tzinfo=(pytz.timezone('Asia/Shanghai')))  # datetime.datetime(2019, 6, 17, 16, 39, 5, 65823, tzinfo=<DstTzInfo 'Asia/Shanghai' LMT+8:06:00 STD>)

time module

time module that provides various of time function

Generally there are two ways to express the time:

1. Timestamp, offset in seconds relative to 1970.1.1 00:00:00, timestamp is unique

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import time
time.time()  # 1560762051.8676867

2. Array, which is struct_time, the struct_time of the same timestamp will be different depending on the time zone

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time.localtime()  # time.struct_time(tm_year=2019, tm_mon=6, tm_mday=17, tm_hour=17, tm_min=1, tm_sec=4, tm_wday=0, tm_yday=168, tm_isdst=0)

Using gmtime() and mktime() methods to convert two kind of time

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time.gmtime(time.time())  # time.struct_time(tm_year=2019, tm_mon=6, tm_mday=17, tm_hour=9, tm_min=1, tm_sec=22, tm_wday=0, tm_yday=168, tm_isdst=0)
time.mktime(time.localtime())  # 1560762097.0

Convert the types between struct_time and string

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time1 = time.strftime("%Y-%m-%d",time.localtime())  # '2019-06-17'
time2 = time.strptime(time1,"%Y-%m-%d")  # time.struct_time(tm_year=2019, tm_mon=6, tm_mday=17, tm_hour=0, tm_min=0, tm_sec=0, tm_wday=0, tm_yday=168, tm_isdst=-1)

datetime module

datetime module provide multiple functions to handle date and time

The classes defined in datetime module:

• datetime.date: An idealized naive date, Attributes: year, month, and day.;
• datetime.time: An idealized time, Attributes: hour, minute, second, microsecond, and tzinfo;
• datetime.datetime: Combination of date and time. Attributes: year, month, day, hour, minute, second, microsecond, and tzinfo;
• datetime.timedelta: A duration expressing the difference between two date, time, or datetime instances to microsecond resolution;
• datetime.tzinfo: Class for time zone information objects;
• datetime.timezone: A class that implements the tzinfo abstract base class as a fixed offset from the UTC;

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import datetime
datetime.datetime.now()  # datetime.datetime(2019, 6, 17, 17, 14, 20, 575740)

Convert the types between datetime and string

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today1 = datetime.datetime.now().strftime("%Y-%m-%d")  # '2019-06-17'
today2 = datetime.datetime.strptime(today,"%Y-%m-%d")  # datetime.datetime(2019, 6, 17, 0, 0)

timedelta Objects:

class datetime.timedelta(days=0, seconds=0, microseconds=0, milliseconds=0, minutes=0, hours=0, weeks=0)

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duration = datetime.timedelta(days=1)  # datetime.timedelta(1)
now = datetime.datetime.now()  # datetime.datetime(2019, 6, 17, 17, 22, 17, 222917)
tomorrow = now + duration  # datetime.datetime(2019, 6, 18, 17, 22, 17, 222917)
yesterday = now - duration  # datetime.datetime(2019, 6, 16, 17, 22, 17, 222917)
duration2 = tomorrow - yesterday  # datetime.timedelta(2)

Conversion between time and datetime

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datetime.datetime.fromtimestamp(time.time())  # datetime.datetime(2019, 6, 17, 17, 24, 35, 111480)

A reference of all the legal format codes: