Python

Crash Courseby Monica Sweat

Python Perspective• is strongly typed, interpreted language

• is used to define scripts(Don't even need to define a function proper.)

• is used to define functions

• can be used in object-oriented style

• is an up and coming real language in industry

Integrated Development Environment: IDLE

• IDLE is provided with standard python installation

• available for virtually any platform

• provides an editing window

• provides an interactive interpreter window

Starting Simply

can use IDLE / python as a calculator>>> 3 + 412>>> 4 ** 216>>> 6 / 23>>> 1 / 20 gotcha that begs an introduction to types

Common Types

• sampling of types– int signed integer, 32 bits, ±2,147,483,647– long arbitrarily long ends with L– float 64 bit double precision, like 1.23 or 7.8e-28

– str delimit in ' or "– bool Booleans True and False

• type(x)yields the type of the data stored currently in variable x

str Type

• str is the type for strings in python• they can be single quote or double quote

delimitedword = "can't"

• multiline strings can be triple quoted (that's 3 single quotes or 3 double quotes in a row)poem = """Roses are red,violets are blue."""

Comments (relates to strings)

• comments in python are single line and use the # symbol

# This program written by George Burdell• multiline comments can be faked by using the

triple quoted string trick

"""This program written by Monica SweatJuly 8, 2008"""

Math Operations

• () parens for grouping• + - unary plus, minus• ** exponentiation• * / % mult-style ops• + - add, subtract

Simple Demo of Variables

>>> age = 18>>> print age18>>> age = age + 1>>> print age19

Python Variables• Python is case-sensitive– variable names– function names– everything

• Camel case is a common style in python, java, etc.firstName = 'George'lastName = 'Burdell'print firstName, lastNameword = "don't"

Python Variables• [a-zA-Z][a-zA-Z0-9 _]*• start with letter followed by letters and digits

• any length• case matters

• do not have to be declared!

• python is strongly typed, but the "type" is bound to the data and not the variable

Script Example

Complete script using variablesAssignment statement uses =

hours = 35rate = 25.50pay = hours * rateprint pay

Printing ResultsIncreasingly better ways to print pay

hours = 35rate = 25.50pay = hours * rateprint payorprint "Your pay is", payorprint "Your pay is $" + str(pay)orprint "Your pay is $%.2f" % pay

Easy User Input

Use input for console input of a numeric value

hours = input("How many hours? ")

rate = input("Pay rate? ")

pay = hours * rate

print "Your pay is $%.2f" % pay

Getting Input from the User

• numeric inputage = input("Age? ")

• string inputname = raw_input("Name? ")

Type Conversion

• x = int(3.9)• y = float(5)• print "Answer: " + str(2 * 3)

(Useful if concatenating with a string)• age = int(raw_input("Age? "))

(Useful if using raw_input to get all input from the user.)

• average = float(sum)/float(total)(Forces float division)

Conditionals

• if• if/else• if/elif/elif/elif/…/else

• all branches use colon :• all bodies are indented

Python uses indentation to denote blocks.

Building Conditions• relational operators as expected<, >, <=, >=, ==, !=, <>(assignment uses single equals sign)

• logical operators are lowercasenot, and, or(! can be used for not)

• parentheses not necessary unless overriding precedence

Conditionals

age = input("Age? ")if age <= 12:ticketPrice = 5

elif age >= 65:ticketPrice = 7.5

else:ticketPrice = 9

print ticketPrice

Defining a Function

def rectangleArea(length, width):

area = length * width

return area

Using Modules

import math

def circleArea(radius):

area = math.pi * radius ** 2

return area

http://docs.python.org/modindex.htmlmath, random, re, os, …

Importing Modules

import mathprint math.pix = math.sqrt(9)

vs.

from math import pi, sqrtprint pix = sqrt(9)

Python Sequences (arrays)

• python's answer to the array• is dynamic• behaves like a linked listed with indexing

names = ["Fred", "Wilma"]

names[0] = "Barney"

print names[0]

Python Sequences (arrays)

common operations (there are many)

names = names + ["Dino"]

or

names.append("Bambam")

for Loop

for-each style iterates through a sequence

syntax:for item in sequence: block-of-code

for flavor in ["chocolate", "vanilla"]:

print "I like", flavor

for Loop

def average(array):

sum = 0

count = 0

for num in array:

sum = sum + num

count = count + 1

return float(sum)/count

Counting-style for Loop

for loop with counting style using range:for num in range(1, 5):

print num

Output:

1

2

3

4

Processing Array without/with range

for-each style to iterate through a sequence:for flavor in ["chocolate", "vanilla"]:

print "I like", flavor

vs.index-driven style processing a sequence:flavors = ["chocolate", "vanilla", "mint"]

for index in range(len(flavors)):

print "I like", flavors[index]

range Function Details• most commonly used to generate indices for iterating a sequence• may have 1, 2, or 3 parameters• stopping value is exclusive>>> range(5) (starts at 0 if one parameter)[0, 1, 2, 3, 4]

>>> range(1995, 2000) (stopping value exclusive)

[1995, 1996, 1997, 1998, 1999]

>>> range(0, 55, 5) (3rd parameter is step value)[0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50]

range Function to Generate Data

def summation(n):

total = 0

for num in range(n + 1):

total = total + num

return total

while Loop

number = 1

while number <= 5:

print number

number += 1

myro – Major Bonuses

• myro defined as a proper module– programmer imports it as they would any module– natural way to incorporate added functionality

• works with standard python– all of standard python is available to the user– other modules: math, random, os, etc are still

available– materials for python still apply