python tutorial descafeinado

7/27/2019 Python Tutorial Descafeinado

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A Caffeinated Crash Course inPython


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Python is not.

Java

C Perl


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The Python Interpreter

Type python at the command prompt

In windows, find the python icon on thestart menu


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Dir and Help

help()

dir()


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Syntax Errors

Python Errors show the line number of

the error

Check the line above if your error makes

no sense


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White Space


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String Basics

Not a mutable data type

String can be delimited with either the

or


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More Strings

Concatenation uses the +

You can do math with strings!


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Output


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Indexing

To index into a string, specify the positioninside square brackets

You can index into a string from the end of

the string.


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Slicing A Substring of a string is a slice

Your head or tail can be a negative

index


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More Slicing

You dont need to specify the beginning

and end of the string

Find the length of a string with len()


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Example


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Lists

Lists in python are made of any data

type delimited by commas and

surrounded by brackets.

Lists are mutable


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More on Lists

You can index into lists

You can slice lists


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Modifying Lists

You can add lists

And append to them


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List Methods

sort - sorts the list in place, returns nothing

sorted - does not modify the list, returns new

sorted list

reverse - reverses the list in place, returnsnothing


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String Formatting

The % operator substitutes values into astring

%s and %d are placeholders for the values

(%d makes sure its a number)

%s has %d letters %

(colorless, len(colorless))

becomes the string colorless has 9

letters


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Converting from

Strings to Lists

Join a list to make a string

Split a string to make a list


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For and If

If statements

For Statements


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List Comprehensions

Applies a function to every element of a

list


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Dictionaries Hash - maps things to things!


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Even More Dictionaries


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Example: Letter Frequencies


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Classes


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Importing and the Python path Import using the import command

You can import everything from a

module using the syntax from

import *


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Files

Filename = /home/havasi/input.txt

input = open(Filename, r)

output = open(Filename + .out, w)for line in input.readlines():

input.write(Cows! \n)

input.close()

output.close()


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Resources Python.org

NLTK Python Tutorial

http://nltk.org/doc/en/programming.html

IDLE (Windows Development Env.)

http://www.python.org/idle/

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