Python Modules and Packages - Prof. Lotfi Ben Othmane, Study notes of Web Design and Development

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Chapter 10: Batteries Included

Lotfi Ben Othmane

Department of Computer Science

Western Michigan University

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Modules

Packages

Standard Library

Roadmap

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1. Modules

Developing Modules

Using Modules

Exploring Modules

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1.1 Develop Modules

Modules are python programs. They could be

imported and used in other modules

Usually modules define functions and classes

Example of a module containing a function

# hello2.py

# hello2.py

def hello():

def hello():

print "Hello, world!"

print "Hello, world!"

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1.2 Using of Modules—Cont.

To use a module we need to import it then use it

Save a module

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1.2 Using of Modules—Cont.

A module may include code to be executed (e.g.,

call of a function)

# ch10_02.py# ch10_02.py

def hello():def hello():

print "Hello, world!" print "Hello, world!"

hello()hello()

Such module when imported execute specified

Such module when imported execute specified

code (see call to method hello())code (see call to method hello())

The module includes a

call to a function

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1.2 Using of Modules—Cont.

Python uses a variable name. In an imported

module, it is set to the name of the module. If the

module is executed it set to main.

The technique could be used to run executable

code only when the module is executed and do not

run the code when the module is imported.

# ch10_03.py

# ch10_03.py

def hello():

def hello():

print "Hello, world!"

print "Hello, world!"

if name='main': hello()

if name='main': hello()

Example of code that

tests if a method

should be executed or

not (not executed if the

module is imported)

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1.2 Using of Modules—Cont.

A second method to make a modules available

(could be imported) is to add the folder where the

module is located in the environment variable

PYTHONPATH

When a module is imported the first time, Python

compiles the program and generates a file with

extension PYC.

PYC files are machine independent compiled

modules

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1.3 Exploring Modules—Cont.

doc variable could be used to get the

documentation about a function

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2. Packages

Modules could be grouped in packages

A package is a directory that includes a set of

modules. It must also include a module with the

name init.py

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2. Packages

Exploring package

email

Exploring

init

module for

email

package

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3. Standard Library

sys module

os module

fileinput module

set, heaps and deques modules

time module

random module

shelve module

re module

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3.2 os Module

Gives access to several operating system services.

Table below gives an example of variables and

functions available in module os

urandom(n) Returns n bytes of cryptographically strong random data

linesep Line separator ('\n', '\r', or '\r\n')

sep Separator used in paths

system(command) Executes an OS command in a subshell

environ Mapping with environment variables

Function/Variable Description

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3.2 os Module--Cont

Example of use of the module

Variable

TMP

Variable

PCBRAND

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3.2 os Module--Cont

Example of use of the module

Command to

start Firefox

from python

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3.3 fileinput Module

Provides variable and functions that enables iterating

over the lines of a text file

Table below gives an example of variables and

functions available in module fileinput

close() Closes the sequence

filelineno() Returns line number within current file

lineno() Returns current (cumulative) line number

filename() Returns name of current file

Facilitates iteration over lines in multiple input

streams

input([files[, inplace[,

backup]])

Function/Variable Description

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3.4 set, heaps and deques Modules

Python integrate some data structures such as

dictionary, lists, and string. It includes some modules

for author data structure such as sets, heaps and

deques.

Sets: constructed from sequence and their main use is

to check membership.

Heap: kind of priority queue. Let add objects in arbitrary

order. It does some operations with efficiency.

Deqeue : double-ended queue. Useful when you need

to remove element in the order they were add.

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Example of use of the set module

3.4 set, heaps and deques Modules—

Cont.

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Set of methods for heap operations

3.4 set, heaps and deques Modules—

Cont.

nsmallest(n, iter)

nlargest(n, iter )

heapreplace(heap,x)

heapify(heap)

heappop(heap)

heappush(heap, x)

Function/Variable

Returns the n smallest elements of iter

Returns the n largest elements of iter

Pops off the smallest element and pushes x

Enforces the heap property on an arbitrary list

Pops off the smallest element in the heap

Pushes x onto the heap

Description

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3.4 set, heaps and deques Modules—

Cont.

Use of heap module

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3.5 time Module—Cont.

Example of the use of the module

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3.6 random Module

Random module contains functions that return random

numbers, which can be useful for simulations for

example.

sample(seq, n)

shuffle(seq[, random])

choice(seq)

randrange([start], stop,

[step])

uniform(a, b)

random()

Function/Variable

Chooses n random, unique elements from the

sequence seq

Shuffles the sequence seq in place

Returns a random element from the sequence seq

Returns a random number from range(start,

stop,step)

Returns a random real number n such that a ≤ n < b

Returns a random real number n such that 0 ≤ n < 1

Description

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3.6 random Module—Cont.

Example of the use of module random to generate a

random date (ch10_2.py)

from random import *

from time import *

date1 = (2008, 1,21, 0, 0, 0, -1, -1, 0)

time1 = mktime(date1)

date2 = (2009, 1, 11, 0, 0, 0, -1, -1, 0)

time2 = mktime(date2)

randomtime = uniform(time1,time2)

asctime(localtime(randomtime))

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3.6 random Module—Cont.

Example of the use of module random to generate

a random numbers (ch10_3.py)

from random importfrom random import randrangerandrange

num =

num = input('How

input('How many dice? ')

many dice? ')

sides =sides = input('Howinput('How many sides per die? ')many sides per die? ')

sum = 0

sum = 0

for i infor i in range(numrange(num): sum +=): sum += randrange(sidesrandrange(sides) + 1) + 1

print 'The result is', sumprint 'The result is', sum

Output of ch10-3.py

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3.7 shelve Module—Cont.

Simple database application using shelve (ch10_4.py)

import sys, shelve

import sys, shelve

defdef store_person(dbstore_person(db):):

Query user for data and store it in the shelf objectQuery user for data and store it in the shelf object

pidpid == raw_input('Enterraw_input('Enter unique ID number: ')unique ID number: ')

person = {}

person = {}

person['nameperson['name'] ='] = raw_input('Enterraw_input('Enter name: ')name: ')

person['ageperson['age'] ='] = raw_input('Enterraw_input('Enter age: ')age: ')

person['phoneperson['phone'] ='] = raw_input('Enterraw_input('Enter phone number: ')phone number: ')

db[piddb[pid] = person] = person

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3.7 shelve Module—Cont.

def

def lookup_person(db

lookup_person(db ):

Query user for ID and desired field, and fetch the corresponQuery user for ID and desired field, and fetch the corresponding datading data

from

from

the shelf objectthe shelf object

pidpid == raw_input('Enterraw_input('Enter ID number: ')ID number: ')

field =field = raw_input('Whatraw_input('What would you like to know? (name, age, phone) ')would you like to know? (name, age, phone) ')

field =field = field.strip().lowerfield.strip().lower()()

printprint field.capitalizefield.capitalize() + ':',() + ':', \

db[pid][fielddb[pid][field]]

defdef print_helpprint_help():():

print 'The available commands are:'print 'The available commands are:'

print 'store : Stores information about a person'

print 'store : Stores information about a person'

print 'lookup : Looks up a person from ID number'print 'lookup : Looks up a person from ID number'

print 'quit : Save changes and exit'

print 'quit : Save changes and exit'

print '? : Prints this message'print '? : Prints this message'

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3.7 shelve Module—Cont.

defdef enter_commandenter_command():():

cmdcmd == raw_input('Enterraw_input('Enter command (? for help): ')command (? for help): ')

cmdcmd == cmd.strip().lowercmd.strip().lower()()

return

return cmd

cmd

def main():def main():

database =database = shelve.open('database.datshelve.open('database.dat')')

try:try:

while True:while True:

cmdcmd == enter_commandenter_command()()

ifif cmdcmd == 'store':== 'store':

store_person(database

store_person(database )

elifelif cmdcmd == 'lookup':== 'lookup':

lookup_person(databaselookup_person(database))

elif

elif cmd

cmd == '?':

print_helpprint_help()()

elifelif cmdcmd == 'quit':== 'quit':

returnreturn

finally:finally:

database.close

database.close ()

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3.7 shelve Module—Cont.

Example of the use of Ch10_4.py