Learn Python in three hours

Overview

History
Installing & Running Python
Names & Assignment
Sequences types: Lists, Tuples, and Strings
Mutability

Brief History of Python

Invented in the Netherlands, early 90s by Guido

Python’s Benevolent Dictator For Life

“Python is an experiment in how much

http://docs.python.org/

The Python tutorial is good!

Running Python

The Python Interpreter

Typical Python implementations offer both an interpreter and compiler
Interactive interface

Installing

Python is pre-installed on most Unix systems, including Linux and MAC

IDLE Development Environment

IDLE is an Integrated DeveLopment Environ-ment for Python, typically

Editing Python in Emacs

Emacs python-mode has good support for editing Python,

Running Interactively on UNIX

On Unix…
% python
>>> 3+3
6
Python prompts with ‘>>>’.
To

Running Programs on UNIX

Call python program via the python interpreter
% python

Example ‘script’: fact.py

#! /usr/bin/python
def fact(x): """Returns the factorial of its argument, assumed

Python Scripts

When you call a python program from the command line

Example of a Script

#! /usr/bin/python
""" reads text from standard input and

results

python> python email0.py bill@msft.com
gates@microsoft.com
steve@apple.com
bill@msft.com
python>

Getting a unique, sorted list

import re
from sys import stdin
pat = re.compile(r'[-\w][-.\w]*@[-\w][-\w.]+[a-zA-Z]{2,4}’)
#

results

python> python email2.py bill@msft.com
gates@microsoft.com
steve@apple.com
python>

Simple functions: ex.py

"""factorial done recursively and iteratively"""
def fact1(n):
ans = 1

Simple functions: ex.py

671> python
Python 2.5.2 …
>>> import ex
>>> ex.fact1(6)
1296
>>> ex.fact2(200)
78865786736479050355236321393218507…000000L
>>> ex.fact1

The Basics

A Code Sample (in IDLE)

x = 34 - 23 #

Enough to Understand the Code

Indentation matters to code meaning
Block structure indicated

Basic Datatypes

Integers (default for numbers)
z = 5 / 2 # Answer

Whitespace

Whitespace is meaningful in Python: especially indentation and placement of newlines
Use

Comments

Start comments with #, rest of line is ignored
Can include a

Assignment

Binding a variable in Python means setting a name to hold

Naming Rules

Names are case sensitive and cannot start with a number.

Naming conventions

The Python community has these recommend-ed naming conventions
joined_lower for functions,

Assignment

You can assign to multiple names at the same time
>>>

Accessing Non-Existent Name

Accessing a name before it’s been properly created (by

Sequence types: Tuples, Lists, and Strings

Sequence Types

Tuple: (‘john’, 32, [CMSC])
A simple immutable ordered sequence of items
Items

Similar Syntax

All three sequence types (tuples, strings, and lists) share much

Sequence Types 1

Define tuples using parentheses and commas
>>> tu = (23,

Sequence Types 2

Access individual members of a tuple, list, or string

Positive and negative indices

>>> t = (23, ‘abc’, 4.56, (2,3), ‘def’)
Positive

Slicing: return copy of a subset

>>> t = (23, ‘abc’, 4.56,

Slicing: return copy of a =subset

>>> t = (23, ‘abc’, 4.56,

Copying the Whole Sequence

[ : ] makes a copy of an

The ‘in’ Operator

Boolean test whether a value is inside a container:
>>>

The + Operator

The + operator produces a new tuple, list, or

The * Operator

The * operator produces a new tuple, list, or

Mutability: Tuples vs. Lists

Lists are mutable

>>> li = [‘abc’, 23, 4.34, 23]
>>> li[1] =

Tuples are immutable

>>> t = (23, ‘abc’, 4.56, (2,3), ‘def’)
>>> t[2]

Operations on Lists Only

>>> li = [1, 11, 3, 4,

The extend method vs +

+ creates a fresh list with

Operations on Lists Only

Lists have many methods, including index, count, remove,

Operations on Lists Only

>>> li = [5, 2, 6, 8]
>>> li.reverse()

Tuple details

The comma is the tuple creation operator, not parens
>>> 1,
(1,)
Python