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Dictionary and Keys

To store values in reference to other values:

dict = {'key1' : 1, 'key2' : 2, 'key3' : 3}

dict is the dictionary variable name

dict [’key1′] will output 1

dict[’key1′] = 5 will add/change the word in dictionary

del dict[’key2′] will delete key2 from the dictionary

For a list within a dictionary:

dict[’list_name’] = [’item1′, ‘item2′, ‘item3′]

dict[’list_name’].remove(’item2′)

print dict[’item1′][0] will print the first item in the list item1

for

In a list:

for var in list_name:

for will cycle through the list, with var taking the value of the component for is “looking at”

In a dictionary:

for var in dictionary:

for will cycle through the dictionary, with var taking the value of the key the for is “looking at”

Lists

list_name = [ "x”, “y”, “z”]

list_name [0] = “x”

to change “x” to “v”: listname [0] = “v”

list_name.append(”a”) adds an a to the end

list [0:2] will output [”x”, “y”], it goes up to but does not include element 2

list[1:] will output [”y” “z”], colon means an index is unnecessary if it goes all the way to beginning or end

list_name.index(”y”) = 1

list_name.insert(index#, string) will insert string at given index number

list_name.sort() puts lists in alphabetical/numerical order

Removing Items from a List

list_name.remove(’item’) will search the list for ‘item’ and then remove item from the list

listname.pop(index) will remove the item at index and return that item

del (listname[index]) will remove the item at index

Datatypes

Strings

Numbers

Booelans

Lists

#pythondictionary

Mistakes

- not including : after if/else

Type

type (argument) will return:

int (if argument is integer)

float (if argument is floating point)

str (if argument is string)

int, float, and str are variables, not strings

#pythondictionary

Importing

“A module is a file that contains definitions—including variables and functions—that you can use once it is imported.”

For example, importing the math module allows for Python to do square roots

To import everything,

import module

To only import specific things from a module,

from module import function

For a specific use,

module.function( )

Math Commands

Exponent: ** (ex. 2 ** 3 = 8)

Remainder: % (ex. 9%4 = 1)

#pythondictionary

Functions

Define a function:

def functionName (inputs) :

interior of function contains commands

Call a function:

functionName( input1, input2, input3...)

If an input is a string, it should not be put in quotes in the input parentheses

#pythondictionary

String Indexing

String indexing starts at 0

string(#) calls on index # in string

string[ 0:len(string) ] calls on all characters in string but can be modified to select just a few (ex. 1:4)

#pythondictionary

String functions

Note: may set var = “string” and perform these functions on var

Length: len(string) will return number of characters

Ensure all characters: string.isalpha() will return boolean, True or False

Lowercase: string.lower()

Uppercase: strong.upper()

str(input) turns input into a string

Concatenation: string1 + string2

#pythondictionary

User Input

var = raw_input(”string to print for user view”)

Example: asking a name

name = raw_input("What’s your name? ")

#pythondictionary

print

print “string”

print ‘string’

print variable

print "%d to the power of %d is %d." % (base, exponent, result)

print “apple: %s” % 3 will print “apple: 3″

#pythondictionary

Boolean Operators

True

False

and

not

or

#pythondictionary #boolean

Comparators

5 > 4

4 < 5

5 == 5

5 != 4

max(argument1, argument2, argument3)

min(argument1, argument2, argument3)

abs(argument)

#pythondictionary #equal #unequal #maximum #minimum

if/else

if var == value:

consequence such as:

print “response”

return True

elif: # short for else if

consequence

else:

consequence

#pythondictionary

Order of Operations

Very First Parentheses

First not

Next and

Last or

#pythondictionary

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