Transcript Python`s standard library

The Standard Library In Python
By Ryan Smith
Python’s “Batteries Included”
Philosophy
 Python’s standard library was designed to be able to handle as
many situations as possible.
 Has a module for just about anything
 Can do email, access the internet, work with csv and xml
packages, and more.
 Chances are if you want to do it, Python has an easier way to
get it done.
The OS Module
 Python contains a number of functions that can interact with
the operating system
 The os module allows us to access them
 Some examples of os commands:
– Returns the current working directory
os.chdir(‘/cs265/Lab1’) – Change current directory
os.system(‘mkdir Lab2’) – Runs from the command
line
 os.getcwd()
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 Must use import os to gain access to the commands
Wildcards
 The glob module allows us to make file lists from wildcard
searches
 To use the command, we must use import
 Example code:
 import glob
 glob.glob(‘*.py’)
 Returns: [‘hello.py’, ‘world.py’, ‘duh.py’]
glob
Getting Command Line Arguments
 Accessing command line arguments can be done using the
sys module.
 The argv attribute allows us to manipulate the arguments.
 For example, take the file tootsie.py:
 import sys
 print(sys.argv)
 Running python tootsie.py one two three from the
command line would produce:
 [‘tootsie.py’, ‘one’, ‘two’, ‘three’]
 We can do more sophisticated processing with argparse
Error Output & Redirection
 The sys module contains the stderr attribute.
 We can use it to give warnings and error messages when
stdout will not work.
 For example:
 sys.stderr.write(‘Dat not gonna work’)
 To terminate a script, we can use sys.exit()
Regular Expressions
 In Python, the re module allows us to use regular
expressions
 For example, the findall command:
 import re
 re.findall(r’\bf[a-z]*’, ‘fee fi fo fum, you
smell’)
 This would return: [‘fee’, ‘fi’, ‘fo’, ‘fum’]
 Command found all words that started with f
 Can also use string methods:
 ‘tea for too’.replace(‘too’, ‘two’)
 Returns ‘tea for two’
The math Module
 Python’s math module allows us to access a number of
complicated operations
 math.cos(), math.log()
 Also, the random module allows us to create random
numbers.
– Chooses 1 value from an inputted list
random.sample(range(100), 10) – Picks a set of
numbers from a specified range
random.random() – Creates a random float
random.randrange(6) – Chooses a random number from
the inputted range
 random.choice()
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Accessing the Internet
 We can retrieve data and send emails using python.
 This requires the urllib.request module and the smtplib
module respectively
Dates and Times
 The datetime module allows the manipulation of dates and
times.
 For example:
 from datetime import date
 now = date.today()
 now
 This would return the current date
 We can also format now with strftime
 now.strftime(“%m-%d-%y)
 Returns 5-30-2014
Data Compression
 We can compress data in python using a multitude of
modules: zlib, gzip, bz2, lzma, zipfile, and
tarfile
 For instance:
 import zlib
 s = b’witch which has which witches wrist
watch’
 len(s)
 41
 t = zlib.compress(s)
 len(t)
 37
Performance Measurement
 The timeit module allows us to track the performance of a
program
 For instance:
 from timeit import Timer
 Timer(‘t=a; a=b; b=t’, ‘a=1; b=2’).timeit()
 Returns .57535828626024577
Quality Control
 The doctest module allows us to test other modules
 For instance, doctest.testmod() allows us to automatically
validate any embedded tests.
 Using the unittest module allows us to create a set of tests
that we can keep in a separate file.
Sources
 Python Course resources #2, Part 10:
 https://docs.python.org/3/tutorial/stdlib.html