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Library in Python

A library is a collection of functions that share a common theme. This loose definition will become clear when we start working with a library.

Using the calendar Library

Consider the following problem:

Problem

In the year 3000, which day of the week will August 15th fall on?

Solution

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import calendar
calendar.prmonth(3000, 8)

Output

When the above code is executed, the output is:

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    August 3000
Mo Tu We Th Fr Sa Su
             1  2  3
 4  5  6  7  8  9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30 31

15th of August falls on a Friday. Isn't that lovely? It took just two lines of code!

The calendar library is one among several libraries in Python's standard library. A comprehensive list can be found here.

In the code, calendar is the name of the library and import is the keyword used to include this library as part of the code. The calendar library is a collection of functions that are related to calendars. The prmonth function accepts <year> and <month> as input and displays the calendar for that month in the specified year.

Note

If we skip the import step:

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# import calendar
calendar.prmonth(3000, 8)

It gives the following error:

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NameError: name 'calendar' is not defined

To access a function defined inside a library, we use the following syntax:

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<library>.<function>(<arguments>)

Alternative Solution

Another way to solve the problem is to use the weekday function:

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import calendar
print(calendar.weekday(3000, 8, 15))

Output

The output of the above code is 4, which means: | Day | Number | |-----------|--------| | Monday | 0 | | Tuesday | 1 | | Wednesday | 2 | | Thursday | 3 | | Friday | 4 | | Saturday | 5 | | Sunday | 6 |

Using the time Library

Let us now try to answer this hypothetical question:

Problem

You are stranded on an island in the middle of the Indian Ocean. The island has a computing device that has just one application installed in it: a Python interpreter. You wish to know the current date and time.

Solution

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from time import ctime
print('The current time is:', ctime())

Output

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The current time is: Fri Apr  2 12:24:43 2021

The syntax of the import statement in line-1 looks different. The from keyword allows us to import a specific function from a library.

This way of importing functions is useful when we need just one or two functions from a given library:

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from time import ctime, sleep
print('Current time is:', ctime())
print('I am going to sleep for 10 seconds')
sleep(10)
print('Current time is:', ctime())

The sleep(x) function in the time library suspends the execution of the program for x seconds. If we would be using several functions in the library, it is better to import the entire library.

The Zen of Python

As a fun exercise, consider the following code:

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import this

Output

This gives the following output:

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The Zen of Python, by Tim Peters

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!

These are some nuggets of wisdom from Tim Peters, a "major contributor to the Python programming language". Some points make immediate sense, such as "readability counts".