Master Python Time: From Timestamps to Advanced Date Manipulation

Preface

This article summarizes common Python time operations, emphasizing the importance of handling timestamps, sleep, local time, and formatting.

time module

Timestamp

Gets the number of seconds elapsed since 1970‑01‑01 00:00:00 UTC.

import time
timestamp = time.time()  # type: float
print(timestamp, type(timestamp))

Result shown below:

Sleep

Pauses program execution for a specified number of seconds.

# Sleep 1 second
time.sleep(1)

Local time

Retrieves the current local time as a struct_time object.

t = time.localtime()  # type: time.struct_time
print(t, type(t))

localtime can also accept a timestamp argument.

# Convert timestamp to struct_time
t = time.localtime(1606395685.1878598)  # type: time.struct_time
print(t, type(t))

Simple time formatting

t = time.ctime()  # type: str
print(t, type(t))

Result shown below:

time.ctime() can also accept a timestamp.

t = time.ctime(1606395685.1878598)  # type: str
print(t, type(t))

Time formatting

Date → string (strftime)

t = time.localtime()  # type: time.struct_time
t_str = time.strftime("%Y-%m-%d", t)  # type: str
print(t_str, type(t_str))

String → date (strptime)

t_str = "2020-11-02"
t_time = time.strptime(t_str, "%Y-%m-%d")  # type: time.struct_time
print(t_time, type(t_time))

Formatting codes

%Y – full year

%m – month (01‑12)

%d – day of month (01‑31)

%H – hour (24‑hour clock, 00‑23)

%M – minute (00‑59)

%S – second (01‑61)

datetime module

Note: datetime and time are different types and should not be mixed.

from datetime import datetime

datetime.today()

t = datetime.today()  # type: datetime
print(t, type(t))
print(t.year)   # year
print(t.month)  # month

datetime.now()

Similar to today(), returns local time.

t = datetime.now()  # type: datetime
print(t, type(t))

datetime.utcnow()

Returns the current UTC time.

t = datetime.utcnow()  # type: datetime
print("UTC time:", t)

Timestamp → datetime

timestamp = time.time()
print(f"timestamp:{timestamp},type:{type(timestamp)}")
t = datetime.fromtimestamp(timestamp)
print(f"t:{t},type:{type(t)}")

datetime → string (strftime)

t = datetime.now()
str_datetime = t.strftime("%Y-%m-%d %H:%M:%S")
print(f"String date:{str_datetime},type:{type(str_datetime)}")

String → datetime (strptime)

str_datetime = "2020-11-29 22:05:20"
t = datetime.strptime(str_datetime, "%Y-%m-%d %H:%M:%S")
print(f"t:{t},type:{type(t)}")

Datetime arithmetic

Adding days is straightforward, but months and years require extra logic.

from datetime import datetime
import datetime as idatetime
t = datetime.now()
print(f"Current time:{t}")
three_day = t + idatetime.timedelta(days=3)
print(f"Three days later:{three_day}")

Free datetime arithmetic with dateutil

Install the python-dateutil package to add months or years.

pip install python-dateutil

from datetime import datetime
from dateutil.relativedelta import relativedelta
t = datetime.now()
print(f"Current time:{t}")
three_time = t + relativedelta(months=3)
print(f"Three months later:{three_time}")
one_year = t + relativedelta(years=1)
print(f"One year later:{one_year}")
up_year = t + relativedelta(years=-1)
print(f"Same time last year:{up_year}")

Conclusion

The article recommends using datetime for most time operations, warns against mixing time and datetime, and highlights the frequent need to convert string dates to datetime objects. The

python-dateutil

relativedelta

methods provide convenient month and year arithmetic.