$ curl cheat.sh/
# Single line comments start with a number symbol.

""" Multiline strings can be written
    using three "s, and are often used
    as comments
"""

####################################################
# 1. Primitive Datatypes and Operators
####################################################

# You have numbers
3  # => 3

# Math is what you would expect
1 + 1  # => 2
8 - 1  # => 7
10 * 2  # => 20
35 / 5  # => 7

# Division is a bit tricky. It is integer division and floors the results
# automatically.
5 / 2  # => 2

# To fix division we need to learn about floats.
2.0  # This is a float
11.0 / 4.0  # => 2.75 ahhh...much better

# Result of integer division truncated down both for positive and negative.
5 // 3  # => 1
5.0 // 3.0  # => 1.0 # works on floats too
-5 // 3  # => -2
-5.0 // 3.0  # => -2.0

# Note that we can also import division module(Section 6 Modules)
# to carry out normal division with just one '/'.
from __future__ import division

11 / 4  # => 2.75  ...normal division
11 // 4  # => 2 ...floored division

# Modulo operation
7 % 3  # => 1

# Exponentiation (x to the yth power)
2 ** 4  # => 16

# Enforce precedence with parentheses
(1 + 3) * 2  # => 8

# Boolean Operators
# Note "and" and "or" are case-sensitive
True and False  # => False
False or True  # => True

# Note using Bool operators with ints
0 and 2  # => 0
-5 or 0  # => -5
0 == False  # => True
2 == True  # => False
1 == True  # => True

# negate with not
not True  # => False
not False  # => True

# Equality is ==
1 == 1  # => True
2 == 1  # => False

# Inequality is !=
1 != 1  # => False
2 != 1  # => True

# More comparisons
1 < 10  # => True
1 > 10  # => False
2 <= 2  # => True
2 >= 2  # => True

# Comparisons can be chained!
1 < 2 < 3  # => True
2 < 3 < 2  # => False

# Strings are created with " or '
"This is a string."
'This is also a string.'

# Strings can be added too!
"Hello " + "world!"  # => "Hello world!"
# Strings can be added without using '+'
"Hello " "world!"  # => "Hello world!"

# ... or multiplied
"Hello" * 3  # => "HelloHelloHello"

# A string can be treated like a list of characters
"This is a string"[0]  # => 'T'

# You can find the length of a string
len("This is a string")  # => 16

# String formatting with %
# Even though the % string operator will be deprecated on Python 3.1 and removed
# later at some time, it may still be good to know how it works.
x = 'apple'
y = 'lemon'
z = "The items in the basket are %s and %s" % (x, y)

# A newer way to format strings is the format method.
# This method is the preferred way
"{} is a {}".format("This", "placeholder")
"{0} can be {1}".format("strings", "formatted")
# You can use keywords if you don't want to count.
"{name} wants to eat {food}".format(name="Bob", food="lasagna")

# None is an object
None  # => None

# Don't use the equality "==" symbol to compare objects to None
# Use "is" instead
"etc" is None  # => False
None is None  # => True

# The 'is' operator tests for object identity. This isn't
# very useful when dealing with primitive values, but is
# very useful when dealing with objects.

# Any object can be used in a Boolean context.
# The following values are considered falsey:
#    - None
#    - zero of any numeric type (e.g., 0, 0L, 0.0, 0j)
#    - empty sequences (e.g., '', (), [])
#    - empty containers (e.g., {}, set())
#    - instances of user-defined classes meeting certain conditions
#      see: https://docs.python.org/2/reference/datamodel.html#object.__nonzero__
#
# All other values are truthy (using the bool() function on them returns True).
bool(0)  # => False
bool("")  # => False


####################################################
# 2. Variables and Collections
####################################################

# Python has a print statement
print "I'm Python. Nice to meet you!"  # => I'm Python. Nice to meet you!

# Simple way to get input data from console
input_string_var = raw_input(
    "Enter some data: ")  # Returns the data as a string
input_var = input("Enter some data: ")  # Evaluates the data as python code
# Warning: Caution is recommended for input() method usage
# Note: In python 3, input() is deprecated and raw_input() is renamed to input()

# No need to declare variables before assigning to them.
some_var = 5  # Convention is to use lower_case_with_underscores
some_var  # => 5

# Accessing a previously unassigned variable is an exception.
# See Control Flow to learn more about exception handling.
some_other_var  # Raises a name error

# if can be used as an expression
# Equivalent of C's '?:' ternary operator
"yahoo!" if 3 > 2 else 2  # => "yahoo!"

# Lists store sequences
li = []
# You can start with a prefilled list
other_li = [4, 5, 6]

# Add stuff to the end of a list with append
li.append(1)  # li is now [1]
li.append(2)  # li is now [1, 2]
li.append(4)  # li is now [1, 2, 4]
li.append(3)  # li is now [1, 2, 4, 3]
# Remove from the end with pop
li.pop()  # => 3 and li is now [1, 2, 4]
# Let's put it back
li.append(3)  # li is now [1, 2, 4, 3] again.

# Access a list like you would any array
li[0]  # => 1
# Assign new values to indexes that have already been initialized with =
li[0] = 42
li[0]  # => 42
li[0] = 1  # Note: setting it back to the original value
# Look at the last element
li[-1]  # => 3

# Looking out of bounds is an IndexError
li[4]  # Raises an IndexError

# You can look at ranges with slice syntax.
# (It's a closed/open range for you mathy types.)
li[1:3]  # => [2, 4]
# Omit the beginning
li[2:]  # => [4, 3]
# Omit the end
li[:3]  # => [1, 2, 4]
# Select every second entry
li[::2]  # =>[1, 4]
# Reverse a copy of the list
li[::-1]  # => [3, 4, 2, 1]
# Use any combination of these to make advanced slices
# li[start:end:step]

# Remove arbitrary elements from a list with "del"
del li[2]  # li is now [1, 2, 3]

# You can add lists
li + other_li  # => [1, 2, 3, 4, 5, 6]
# Note: values for li and for other_li are not modified.

# Concatenate lists with "extend()"
li.extend(other_li)  # Now li is [1, 2, 3, 4, 5, 6]

# Remove first occurrence of a value
li.remove(2)  # li is now [1, 3, 4, 5, 6]
li.remove(2)  # Raises a ValueError as 2 is not in the list

# Insert an element at a specific index
li.insert(1, 2)  # li is now [1, 2, 3, 4, 5, 6] again

# Get the index of the first item found
li.index(2)  # => 1
li.index(7)  # Raises a ValueError as 7 is not in the list

# Check for existence in a list with "in"
1 in li  # => True

# Examine the length with "len()"
len(li)  # => 6

# Tuples are like lists but are immutable.
tup = (1, 2, 3)
tup[0]  # => 1
tup[0] = 3  # Raises a TypeError

# You can do all those list thingies on tuples too
len(tup)  # => 3
tup + (4, 5, 6)  # => (1, 2, 3, 4, 5, 6)
tup[:2]  # => (1, 2)
2 in tup  # => True

# You can unpack tuples (or lists) into variables
a, b, c = (1, 2, 3)  # a is now 1, b is now 2 and c is now 3
d, e, f = 4, 5, 6  # you can leave out the parentheses
# Tuples are created by default if you leave out the parentheses
g = 4, 5, 6  # => (4, 5, 6)
# Now look how easy it is to swap two values
e, d = d, e  # d is now 5 and e is now 4

# Dictionaries store mappings
empty_dict = {}
# Here is a prefilled dictionary
filled_dict = {"one": 1, "two": 2, "three": 3}

# Look up values with []
filled_dict["one"]  # => 1

# Get all keys as a list with "keys()"
filled_dict.keys()  # => ["three", "two", "one"]
# Note - Dictionary key ordering is not guaranteed.
# Your results might not match this exactly.

# Get all values as a list with "values()"
filled_dict.values()  # => [3, 2, 1]
# Note - Same as above regarding key ordering.

# Get all key-value pairs as a list of tuples with "items()"
filled_dict.items()  # => [("one", 1), ("two", 2), ("three", 3)]

# Check for existence of keys in a dictionary with "in"
"one" in filled_dict  # => True
1 in filled_dict  # => False

# Looking up a non-existing key is a KeyError
filled_dict["four"]  # KeyError

# Use "get()" method to avoid the KeyError
filled_dict.get("one")  # => 1
filled_dict.get("four")  # => None
# The get method supports a default argument when the value is missing
filled_dict.get("one", 4)  # => 1
filled_dict.get("four", 4)  # => 4
# note that filled_dict.get("four") is still => None
# (get doesn't set the value in the dictionary)

# set the value of a key with a syntax similar to lists
filled_dict["four"] = 4  # now, filled_dict["four"] => 4

# "setdefault()" inserts into a dictionary only if the given key isn't present
filled_dict.setdefault("five", 5)  # filled_dict["five"] is set to 5
filled_dict.setdefault("five", 6)  # filled_dict["five"] is still 5

# Sets store ... well sets (which are like lists but can contain no duplicates)
empty_set = set()
# Initialize a "set()" with a bunch of values
some_set = set([1, 2, 2, 3, 4])  # some_set is now set([1, 2, 3, 4])

# order is not guaranteed, even though it may sometimes look sorted
another_set = set([4, 3, 2, 2, 1])  # another_set is now set([1, 2, 3, 4])

# Since Python 2.7, {} can be used to declare a set
filled_set = {1, 2, 2, 3, 4}  # => {1, 2, 3, 4}

# Add more items to a set
filled_set.add(5)  # filled_set is now {1, 2, 3, 4, 5}

# Do set intersection with &
other_set = {3, 4, 5, 6}
filled_set & other_set  # => {3, 4, 5}

# Do set union with |
filled_set | other_set  # => {1, 2, 3, 4, 5, 6}

# Do set difference with -
{1, 2, 3, 4} - {2, 3, 5}  # => {1, 4}</