00_python_refresher.py

'''
Multi-line comments go between three  quotation marks.
You can use single or double quotes, but NOT BOTH AT ONCE.
'''

# One-line comments come after the pound symbol



##### BASIC DATA TYPES ######

x = 5               # creates an object
type(5)             # assigning it to a variable is not required
type(5.0)           # float
type('five')        # str , single or double quotes
type(True)          # bool
5 / 2               # integer division ignores remainder
5 / 2.0             # the presence of a decimal means float division


###### LISTS ######

nums = [5, 5.0, 'five']     # multiple data types
nums                        # print the list
type(nums)                  # check the type: list
len(nums)                   # check the length: 3
nums[0]                     # print first element
nums[-1]                    # prints last element in the list
nums[2] = 6                 # replace a list element
nums                        # IT CHANGED
nums.append(7)              # list 'method' that changes the list
nums.remove(5)              # another list method
nums.append(5)
nums.append("apple")
nums.remove("apple")
sorted(nums)                # 'function' that does not modify the list
sorted(nums, reverse=True)  # optional argument
sum(nums)                   # returns sum of a list of numbers
'''
note that list methods are a part of lists, like append and remove
but sorted is a built in python method that TAKES IN a list
'''

# let's use a for loop to "iterate" over this list
days_of_the_week = ['Monday', "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", 'Sunday']

# list slicing
weekdays = days_of_the_week[0:5]    # weekdays, NOTE doesn't include the index 5
weekdays[0:2]  # Start from Index 0 (first) until Index 2 (not inclusive)
days_of_the_week[5:]     # weekends
days_of_the_week[:5]
days_of_the_week[0:7:3]  # the third element means every second element

###### Tuples ######
'''
Tuples are basically lists that can never be changed. You can think of them as light weight lists also.
Lists can grow and shrink via append, insert and remove.
Sometimes we don't want our list to be changed. That's what tuples are for.
If you try to append or remove elements in a tuple, you will get an Traceback error.

Technically, lists are mutable objects and tuples are immutable objects.
Mutable objects can change (think of mutations), and immutable objects can not change.
'''

# range
range(10)  # range function creates a list of 10 items (0 - 9)


##### CONDITIONALS ######

# we will use an if else to implement logic
x              # remember x?
if x  > 10:
    print "x is more than 10 !"  # print adds a new line character to the end
    print "hooray"
elif x > 100:
    print "x is HUGE"

#as soon as one conditional is satisfied, it stops checking!


temperature = 20
if temperature <= 32:
    print "water is ice"
elif temperature > 32 and temperature < 212:
    print "water is liquid"
else:                        #implicity means else if temperature >=212
    print "water will boil"


###### DICTIONARIES ######
'''
have a key value structure,
like a dictionary! :)

dictionary = {
    key1: value1,
    key2: value2,
    ....
}
'''

sinan = {
    "age" : 23,
    "location" : "Baltimore",
    "gender": "Male",
    "occupation": "Professor/Entrepreneur"
}

sinan['age']
sinan['location']

deniz = {
    "age" : 29,
    "location" : "Washington, D.C.",
    "gender": "Female",
    'occupation': "Security Analyst"
}

people = [sinan, deniz] #is a list of myself

people[0] # is the dictionary thar represents sinan
people[0]['age']

'''
for loops are a way of "iterating" over an item, like a list!
but also dictionaries!
'''

# iterating over a list
for day in days_of_the_week: # the "day" variable can really be called anything
    print "the day is " + day

for person in people:
    print type(person)
    print str(person['age']) + " and lives in "+person['location']




sinan.items()             # produces a list
sinan.items()[0][0]

# NOW I can iterate over sinan.items()
# iterating over a dictionaries "items"
for element in sinan.items():
    print element[0]

for first, second in sinan.items():
    print second

# Let's filter out some days based on an if!
for day in days_of_the_week: # the "day" variable can really be called anything
    if len(day) <= 6: #will only print days with length of 6 or less
        print day

##### LIST COMPREHENSIONS ######


import math				# import statement

flubber = [2, 5, 7, 4, 2, 5]
len(flubber)
[n**2 for n in flubber]    # list comprehension
[y / 2.0 for y in flubber] #note the 2.0 instead of 2
[math.sqrt(r) for r in flubber]
'''
note I used a different variable name for each one
because it doesn't matter!
'''

###### FUNCTIONS #######

def give_me_five():         # function definition ends with colon
    print "I'm going to give you five"
    return 5                # indentation required for function body
print "gave you five"
give_me_five()              # prints the return value (5)
a_new_variable = give_me_five()        # assigns return value to a variable, doesn't print it


def calc(x=1, y=2, op = "add"):         # three arguments (without any defaults)
    if op == 'add':                     # conditional statement
        return x + y
    elif op == 'subtract':
        return x - y
    elif op == "multiply":
        return x * y
    else:
        print 'Valid operations: add, subtract, multiply'

calc(5, 3, 'add')
calc(5, 3, 'subtract')
calc(5, 3, 'multiply')
calc([1,2],[3,4], "add")
#calc("sinan",[1,2], "add")    # will not work
calc(5, 3)                    # defaults to add

calc()                        # defaults everything!


point_1 = (1, 2, 2)   #tuples have a paranthesis
point_2  = (3, 4, 5)

pairs = zip(point_1, point_2)
for x in pairs:
    print x
    print x[0]
    print x[1]

[x[0] for x in pairs]