python basics 1

python_basics_1.py

print("\n## We'll run main.py ##\n")
# using the terminal command python 'program name'
# in this case 'python main.py'
# we don't use printf anymore instead:

print("hello, world")

# notice we don't need the ';'
# it is not needed anymore in python

print("\n## function calls do not require the data types ##\n")
# and function definitions use the def keyword

def myfunction():
  print("hello myfunction")
  x = 1
  print(x)
  y = "hello my string variable"
  print(y)

myfunction()

# notice we don't need '{}' for our function anymore
# just a colon ':'
# we also do not specify the type being returned
# everything inside 'myfunction' is indented 4 spaces


print("\n## using the keyword 'True' gives us an infinite loop ##\n")
while True:
  print("hello forever loop")
  break

# however using break it will only run once


print("\n## looping something a certain amount of times can be done ##\n")
# using the 'range()' function
for i in range(10):
  if i < 8:
    print(i)
  elif i == 8:
    print(i)
  else:
    print("9...done with our range!")

# also notice we can write if statments without '()'
# which is kind of weird at first but less typing!


print("\n## data types in python ##\n")
# bool, float, int, and string
# we can use the typeof() function and print() together
# to check types

my_bool = type(True)
my_float = type(3.14)
my_int = type(42)
my_string = type("hello string")

print(my_bool)
print(my_float)
print(my_int)
print(my_string)

# cs50 gives us some helper functions in a library
# similar to using #include in C
# we'll touch on those when we use them in a problem set
# they will allow us to 'get' each of the types
# we just mentioned above


print("\n## There are other types built into python ##\n")
# so you don't have to implement them from scratch


# here are the ones mentioned:

print("\n## complex ##\n")
# The python reference just tells me to ignore this type
# if I have no idea what it is used for. I have no idea how
# this works but this function has something to get you started.
# maybe more for engineers and mathematicians
print(complex(1, 2))


print("\n## dict (dictionary) ##\n")
# pythons version of a hash table
# nothing super complex this is a key/value store
# keep in mind the key should always be unique

my_dictionary = {"red": 57, "blue": 42, 9: "foo"}

for key in my_dictionary:
  print("key:",key)

print(my_dictionary)
print(my_dictionary["blue"])
print(my_dictionary[9])


print("\n## list ##\n")
# pythons version of an array
# remember it is zero base indexed

my_list = [1,2,3,4,5]

print(my_list)
print(my_list[0])


print("\n## range ##\n")
# documentation online states this is
# "a list of arithmetic progressions."
# not actually a list because it is not
# a concrete sequence. You call each index on
# demand. Use the list() function
# to store each value into a list
# it is kind of confusing until you use it
# range() can take up to three arguments

# one argument: just the number to stop at
# not including itself (it will start at zero)

# return a list up to but not including 10

myRange = list(range(10))

print(myRange)

print("\nin a loop the range function will give us each value\n")
# on demand. Meaning not in a list stored in memory

for i in range(3):
  print(i)

# two arguments: the starting number which is included,
# the stop number which is not included in the results

myRange = range(1, 11)
myRangeList = list(myRange) 

print("\n", myRangeList)

# three arguments: start, stop, step
# using step allows us to move the sequence
# in multiples of any number within the range

myRange = range(0, 21, 4)
myRangeList = list(myRange)

print("\n", myRangeList)

myRange = range(0, 21, 2)
myRangeList = list(myRange)

print("\n", myRangeList)


#### set
print("\n## set ##\n")
# mutable (able to change) unordered collections of unique elements
# you have to have unique elements
# you have to run the set() function
# that's because the function takes each item
# and creates a hash table using a hashing function

mySet = set(["boo", "baz", "Mississippi"])
print(mySet)

# we add and remove using the add and remove

# the add() method works when adding a single element to the set
mySet.add("foo")
print(mySet)

# the remove() method raises an error
# if the item is not found which stops
# the program
mySet.remove("Mississippi")

# the discard() method does not throw any errors!
mySet.discard("nope")

print(mySet)


# a common use for a set is to take a list with duplicates
# and create a set of only unique elements
# very handy!

myList = ["zip", "boing", "thwap", "thwap", "bam", "bam"]
print(myList)
mySet = set(myList)
print(mySet)



#### tuple
print("\n## tuple ##\n")
# a tuple is like a list but immutable
# a list can change after being created
print("a tuple can not change after being created")

my_data = ("zero", "one", "two")
print(my_data[1])


# tuple can be rewritten but not modified example mydate[0] = "nope"
my_data = ("tomato", "bacon")


# looping through a tuple
for x in my_data:
  print (x)


if "bacon" in my_data:
  print("true")

print(len(my_data))

# tuple can be deleted but not modified
del my_data

# you can also create a tuple() using the tuple() constructor

my_data = tuple(("apple", "banana", "cherry"))
print(my_data)


# packing is a little weird...
# if we have a bunch of variables we can
# reassign them in bulk using packing and unpacking
# so we are "packing" a bunch of variables into a tuple
# and "unpacking" into the tuple of values on the other side
# now each one is assigned to each value on the other side
# both sides must have the same number of values

v1 = 'x'
v2 = 'y'
v3 = 'z'

# reassigning each value
(v1, v2, v3) = my_data
print(v1)


# we can do this with 2 brand new tuples
# a tuple of empty variables and a tuples of values to assign
# we don't need parenthesis when we do this

a, b, c = 'foo', 'baz', 'bar'
print(a)

# swapping values is one case where this is very useful
# because we don't need a temp variable anymore

# if we want the above variables a and b to swap we just
# pack and unpack them swapped

# this is actually pretty cool
a, b = b, a
print(a)