Python: Basics

• Single-line comment

# Hello World

• Multiple-line comment

""""Hello
World"""

• Functions

.isalpha()	# Check if alpha characters

• Create a function

def <function_name> ():

def <function_name> (arg):

def <function_name> (arg1, arg2):

def <function_name> (*args): # Multiple/unknown # of arguments, arbitrary number of arguments

sum(args)  # You add arguments up

• Import defined functions

from <module> import <function>
Sample:
import math  		#  Import all, use math.sqrt 
math import sqrt  	# Import only sqrt, no need to qualify
from math import *	# Just import metadata??

import this 		# Easter Egg - The Zen of Python

• If-then-else on one line

Boolean = True if (1 == 2) else False

if    :
elif   :
else:

• List

<list_name> = []   # Empty list
<list_name>.append(<item>)

• List samples

my_list.index("dog")  # Return the first index that contains the string “dog”
my_list.insert(4,"cat") # Add item “cat” at index 4 and bump the rest forward

• For loop the list

my_list = [1,9,3,8,5,7]
for number in my_list:
	print number * 2

my_list.sort()

Remove item from the list

• n.pop(index) will remove the item at index from the list and return it to you:

n = [1, 3, 5]
n.pop(1)
# Returns 3 (the item at index 1)
print n
# prints [1, 5]

• n.remove(item) will remove the actual item if it finds it:

n.remove(1)
# Removes 1 from the list,
# NOT the item at index 1
print n
# prints [3, 5]

• del(n[1] is like .pop in that it will remove the item at the given index, but it won't return it:

del(n[1])
# Doesn't return anything
print n
# prints [1, 5]

• Dictionary

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

• Dictionary sample

menu = {} # Empty dictionary
menu['Chicken Alfredo'] = 14.50 # Adding new key-value pair

def plane_ride_cost(city):
    data = {"Charlotte": 183, "Tampa": 220, "Pittsburgh": 222, "Los Angeles": 475}
    return data[city]

Remove item in dictionary

• del deletes a key and its value based on the key you tell it to delete

del dict_name[key_name]

• .remove() removes a key and its value based on the value you tell it to delete.

my_list.remove(value)

• More dictionary samples

inventory = {'gold' : 500,
'pouch' : ['flint', 'twine', 'gemstone'], # Assigned a new list to 'pouch' key
'backpack' : ['xylophone','dagger', 'bedroll','bread loaf']}

# Adding a key 'burlap bag' and assigning a list to it
inventory['burlap bag'] = ['apple', 'small ruby', 'three-toed sloth']

# Sorting the list found under the key 'pouch'
inventory['pouch'].sort()
# Here the dictionary access expression takes the place of a list name

inventory['pocket'] = ['seashell', 'strange berry', 'lint']
inventory['backpack'].sort()

inventory['backpack'].remove('dagger')

inventory['gold'] = inventory['gold']+50

• Dictionaries are unordered

d => {"foo" : "bar"}

for key in d: 
    print d[key]  # prints "bar" 

• Print vertically

for letter in "Codecademy":
	print letter

C
o
d
e
c
a
d
e
m
y

def average(alist):
	return sum(alist)/len(alist)

score = round(score)

• Random module

from random import randrange

# Generate a 
random_number = randrange(1, 10)

• Enumerate

choices = ['pizza', 'pasta', 'salad', 'nachos']

print 'Your choices are:'
for index, item in enumerate(choices):
	print index+1, item

• Zip
  • It's also common to need to iterate over two lists at once. This is where the built-in zip function comes in handy.
  • Zip will create pairs of elements when passed two lists, and will stop at the end of the shorter list.
  • Zip can handle three or more lists as well!

list_a = [3, 9, 17, 15, 19]
list_b = [2, 4, 8, 10, 30, 40, 50, 60, 70, 80, 90]

for a, b in zip(list_a, list_b):
	# Add your code here!
	print a, b