primitives.py

# 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

# Except division which defaults to rounding down
# [Adam] In python2 this would be an integer division ( => 7)
35 / 5  # => 7.0

# 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

# When one of the inputs is a float, result is a float
10.0 / 3  # => 3.3333333333333335

# Modulo operation
7 % 3  # => 1

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

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

# Boolean values are primitives (Note: the capitalization)
True
False

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

# 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

# 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

# (is vs. ==) is checks if two variables refer to the same object, but == checks
# if the objects pointed to have the same values.
# [Adam] this behavior of operators is fairly similar to what exists in java (== vs .equals() )
a = [1, 2, 3, 4]  # Point a at a new list, [1, 2, 3, 4]
b = a             # Point b at what a is pointing to
b is a            # => True, a and b refer to the same object
b == a            # => True, a's and b's objects are equal
b = [1, 2, 3, 4]  # Point b at a new list, [1, 2, 3, 4]
b is a            # => False, a and b do not refer to the same object
b == a            # => True, a's and b's objects are equal

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

# Strings can be added too! But try not to do this.
"Hello " + "world!"  # => "Hello world!"
# Strings can be added without using '+'
"Hello " "world!"    # => "Hello world!"

# 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

# .format can be used to format strings, like this:
"{} can be {}".format("Strings", "interpolated")  # => "Strings can be interpolated"

# You can repeat the formatting arguments to save some typing.
"{0} be nimble, {0} be quick, {0} jump over the {1}".format("Jack", "candle stick")
# => "Jack be nimble, Jack be quick, Jack jump over the candle stick"

# You can use keywords if you don't want to count.
"{name} wants to eat {food}".format(name="Bob", food="lasagna")  # => "Bob wants to eat lasagna"

# If your Python 3 code also needs to run on Python 2.5 and below, you can also
# still use the old style of formatting:
"%s can be %s the %s way" % ("Strings", "interpolated", "old")  # => "Strings can be interpolated the old way"


# None is an object
None  # => None

# Don't use the equality "==" symbol to compare objects to None
# Use "is" instead. This checks for equality of object identity.
"etc" is None  # => False
None is None   # => True

# None, 0, and empty strings/lists/dicts all evaluate to False.
# All other values are True
bool(0)   # => False
bool("")  # => False
bool([])  # => False
bool({})  # => False