Merge remote-tracking branch 'adambard/master'

Conflicts:
	swift.html.markdown

1 files changed, 277 insertions, 134 deletions

diff --git a/python3.html.markdown b/python3.html.markdown
index 0b4feccc..1f9d0e42 100644
--- a/python3.html.markdown
+++ b/python3.html.markdown
@@ -4,6 +4,8 @@ contributors:
     - ["Louie Dinh", "http://pythonpracticeprojects.com"]
     - ["Steven Basart", "http://github.com/xksteven"]
     - ["Andre Polykanine", "https://github.com/Oire"]
+    - ["Zachary Ferguson", "http://github.com/zfergus2"]
+    - ["evuez", "http://github.com/evuez"]
 filename: learnpython3.py
 ---
 
@@ -13,7 +15,7 @@ executable pseudocode.
 
 Feedback would be highly appreciated! You can reach me at [@louiedinh](http://twitter.com/louiedinh) or louiedinh [at] [google's email service]
 
-Note: This article applies to Python 3 specifically. Check out the other tutorial if you want to learn the old Python 2.7
+Note: This article applies to Python 3 specifically. Check out [here](http://learnxinyminutes.com/docs/python/) if you want to learn the old Python 2.7
 
 ```python
 
@@ -32,50 +34,50 @@ Note: This article applies to Python 3 specifically. Check out the other tutoria
 3  # => 3
 
 # Math is what you would expect
-1 + 1  # => 2
-8 - 1  # => 7
+1 + 1   # => 2
+8 - 1   # => 7
 10 * 2  # => 20
 
-# Except division which returns floats by default
+# Except division which returns floats, real numbers, by default
 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
+# 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 you use a float, results are floats
-3 * 2.0 # => 6.0
+3 * 2.0  # => 6.0
 
 # Modulo operation
-7 % 3 # => 1
+7 % 3  # => 1
 
-# Exponentiation (x to the yth power)
-2**4 # => 16
+# Exponentiation (x**y, x to the yth power)
+2**4  # => 16
 
 # Enforce precedence with parentheses
 (1 + 3) * 2  # => 8
 
-# Boolean values are primitives
+# Boolean values are primitives (Note: the capitalization)
 True
 False
 
 # negate with not
-not True  # => False
+not True   # => False
 not False  # => True
 
 # Boolean Operators
 # Note "and" and "or" are case-sensitive
-True and False #=> False
-False or True #=> True
+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
+0 and 2     # => 0
+-5 or 0     # => -5
+0 == False  # => True
+2 == True   # => False
+1 == True   # => True
 
 # Equality is ==
 1 == 1  # => True
@@ -95,29 +97,41 @@ False or True #=> True
 1 < 2 < 3  # => True
 2 < 3 < 2  # => False
 
+# (is vs. ==) is checks if two variable refer to the same object, but == checks
+# if the objects pointed to have the same values.
+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 a 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'
 
 # .format can be used to format strings, like this:
-"{} can be {}".format("strings", "interpolated")
+"{} 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"
+# => "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"
+"{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")
+"%s can be %s the %s way" % ("Strings", "interpolated", "old")  # => "Strings can be interpolated the old way"
 
 
 # None is an object
@@ -126,14 +140,14 @@ 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 is None   # => True
 
 # None, 0, and empty strings/lists/dicts all evaluate to False.
 # All other values are True
-bool(0)  # => False
+bool(0)   # => False
 bool("")  # => False
-bool([]) #=> False
-bool({}) #=> False
+bool([])  # => False
+bool({})  # => False
 
 
 ####################################################
@@ -141,9 +155,17 @@ bool({}) #=> False
 ####################################################
 
 # Python has a print function
-print("I'm Python. Nice to meet you!")
+print("I'm Python. Nice to meet you!")  # => I'm Python. Nice to meet you!
+
+# By default the print function also prints out a newline at the end.
+# Use the optional argument end to change the end character.
+print("Hello, World", end="!")  # => Hello, World!
+
+# Simple way to get input data from console
+input_string_var = input("Enter some data: ") # Returns the data as a string
+# Note: In earlier versions of Python, input() method was named as raw_input()
 
-# No need to declare variables before assigning to them. 
+# No need to declare variables before assigning to them.
 # Convention is to use lower_case_with_underscores
 some_var = 5
 some_var  # => 5
@@ -168,7 +190,7 @@ li.pop()        # => 3 and li is now [1, 2, 4]
 li.append(3)    # li is now [1, 2, 4, 3] again.
 
 # Access a list like you would any array
-li[0]  # => 1
+li[0]   # => 1
 # Look at the last element
 li[-1]  # => 3
 
@@ -177,52 +199,74 @@ 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]
+li[1:3]   # => [2, 4]
 # Omit the beginning
-li[2:]  # => [4, 3]
+li[2:]    # => [4, 3]
 # Omit the end
-li[:3]  # => [1, 2, 4]
+li[:3]    # => [1, 2, 4]
 # Select every second entry
 li[::2]   # =>[1, 4]
-# Revert the list
-li[::-1]   # => [3, 4, 2, 1]
+# Return a reversed copy of the list
+li[::-1]  # => [3, 4, 2, 1]
 # Use any combination of these to make advanced slices
 # li[start:end:step]
 
+# Make a one layer deep copy using slices
+li2 = li[:]  # => li2 = [1, 2, 4, 3] but (li2 is li) will result in false.
+
 # Remove arbitrary elements from a list with "del"
-del li[2]   # li is now [1, 2, 3]
+del li[2]  # li is now [1, 2, 3]
+
+# Remove first occurrence of a value
+li.remove(2)  # li is now [1, 3]
+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] again
+
+# Get the index of the first item found
+li.index(2)  # => 3
+li.index(4)  # Raises a ValueError as 4 is not in the list
 
 # You can add lists
 # Note: values for li and for other_li are not modified.
-li + other_li   # => [1, 2, 3, 4, 5, 6] 
+li + other_li  # => [1, 2, 3, 4, 5, 6]
 
 # Concatenate lists with "extend()"
-li.extend(other_li)   # Now li is [1, 2, 3, 4, 5, 6]
+li.extend(other_li)  # Now li is [1, 2, 3, 4, 5, 6]
 
 # Check for existence in a list with "in"
-1 in li   # => True
+1 in li  # => True
 
 # Examine the length with "len()"
-len(li)   # => 6
+len(li)  # => 6
 
 
 # Tuples are like lists but are immutable.
 tup = (1, 2, 3)
-tup[0]   # => 1
+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
+# Note that a tuple of length one has to have a comma after the last element but
+# tuples of other lengths, even zero, do not.
+type((1))   # => <class 'int'>
+type((1,))  # => <class 'tuple'>
+type(())    # => <class 'tuple'>
+
+# You can do most of the list operations 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
+a, b, c = (1, 2, 3)  # a is now 1, b is now 2 and c is now 3
+# You can also do extended unpacking
+a, *b, c = (1, 2, 3, 4)  # a is now 1, b is now [2, 3] and c is now 4
 # Tuples are created by default if you leave out the parentheses
 d, e, f = 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
+e, d = d, e  # d is now 5 and e is now 4
 
 
 # Dictionaries store mappings
@@ -230,71 +274,96 @@ empty_dict = {}
 # Here is a prefilled dictionary
 filled_dict = {"one": 1, "two": 2, "three": 3}
 
+# Note keys for dictionaries have to be immutable types. This is to ensure that
+# the key can be converted to a constant hash value for quick look-ups.
+# Immutable types include ints, floats, strings, tuples.
+invalid_dict = {[1,2,3]: "123"}  # => Raises a TypeError: unhashable type: 'list'
+valid_dict = {(1,2,3):[1,2,3]}   # Values can be of any type, however.
+
 # Look up values with []
-filled_dict["one"]   # => 1
+filled_dict["one"]  # => 1
 
-# Get all keys as a list with "keys()". 
-# We need to wrap the call in list() because we are getting back an iterable. We'll talk about those later.
-# Note - Dictionary key ordering is not guaranteed.
-# Your results might not match this exactly.
-list(filled_dict.keys())   # => ["three", "two", "one"]
+# Get all keys as an iterable with "keys()". We need to wrap the call in list()
+# to turn it into a list. We'll talk about those later.  Note - Dictionary key
+# ordering is not guaranteed. Your results might not match this exactly.
+list(filled_dict.keys())  # => ["three", "two", "one"]
 
 
-# Get all values as a list with "values()". Once again we need to wrap it in list() to get it out of the iterable.
-# Note - Same as above regarding key ordering.
-list(filled_dict.values())   # => [3, 2, 1]
+# Get all values as an iterable with "values()". Once again we need to wrap it
+# in list() to get it out of the iterable. Note - Same as above regarding key
+# ordering.
+list(filled_dict.values())  # => [3, 2, 1]
 
 
 # Check for existence of keys in a dictionary with "in"
-"one" in filled_dict   # => True
-1 in filled_dict   # => False
+"one" in filled_dict  # => True
+1 in filled_dict      # => False
 
 # Looking up a non-existing key is a KeyError
-filled_dict["four"]   # KeyError
+filled_dict["four"]  # KeyError
 
 # Use "get()" method to avoid the KeyError
-filled_dict.get("one")   # => 1
-filled_dict.get("four")   # => None
+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
+filled_dict.get("four", 4)  # => 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
 
 # Adding to a dictionary
-filled_dict.update({"four":4}) #=> {"one": 1, "two": 2, "three": 3, "four": 4}
-#filled_dict["four"] = 4  #another way to add to dict
+filled_dict.update({"four":4})  # => {"one": 1, "two": 2, "three": 3, "four": 4}
+#filled_dict["four"] = 4        #another way to add to dict
 
 # Remove keys from a dictionary with del
 del filled_dict["one"]  # Removes the key "one" from filled dict
 
+# From Python 3.5 you can also use the additional unpacking options
+{'a': 1, **{'b': 2}}  # => {'a': 1, 'b': 2}
+{'a': 1, **{'a': 2}}  # => {'a': 2}
+
+
 
 # Sets store ... well sets
 empty_set = set()
 # Initialize a set with a bunch of values. Yeah, it looks a bit like a dict. Sorry.
-some_set = {1, 1, 2, 2, 3, 4}   # some_set is now {1, 2, 3, 4}
+some_set = {1, 1, 2, 2, 3, 4}  # some_set is now {1, 2, 3, 4}
 
-#Can set new variables to a set
+# Similar to keys of a dictionary, elements of a set have to be immutable.
+invalid_set = {[1], 1}  # => Raises a TypeError: unhashable type: 'list'
+valid_set = {(1,), 1}
+
+# Can set new variables to a set
 filled_set = some_set
 
-# Add one more item to the set 
-filled_set.add(5)   # filled_set is now {1, 2, 3, 4, 5}
+# Add one more item to the 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}
+filled_set & other_set  # => {3, 4, 5}
 
 # Do set union with |
-filled_set | other_set   # => {1, 2, 3, 4, 5, 6}
+filled_set | other_set  # => {1, 2, 3, 4, 5, 6}
 
 # Do set difference with -
-{1, 2, 3, 4} - {2, 3, 5}   # => {1, 4}
+{1, 2, 3, 4} - {2, 3, 5}  # => {1, 4}
+
+# Do set symmetric difference with ^
+{1, 2, 3, 4} ^ {2, 3, 5}  # => {1, 4, 5}
+
+# Check if set on the left is a superset of set on the right
+{1, 2} >= {1, 2, 3} # => False
+
+# Check if set on the left is a subset of set on the right
+{1, 2} <= {1, 2, 3} # => True
 
 # Check for existence in a set with in
 2 in filled_set   # => True
-10 in filled_set   # => False
+10 in filled_set  # => False
+
 
 
 ####################################################
@@ -326,7 +395,7 @@ for animal in ["dog", "cat", "mouse"]:
     print("{} is a mammal".format(animal))
 
 """
-"range(number)" returns a list of numbers
+"range(number)" returns an iterable of numbers
 from zero to the given number
 prints:
     0
@@ -338,6 +407,30 @@ for i in range(4):
     print(i)
 
 """
+"range(lower, upper)" returns an iterable of numbers
+from the lower number to the upper number
+prints:
+    4
+    5
+    6
+    7
+"""
+for i in range(4, 8):
+    print(i)
+
+"""
+"range(lower, upper, step)" returns an iterable of numbers
+from the lower number to the upper number, while incrementing
+by step. If step is not indicated, the default value is 1.
+prints:
+    4
+    6
+    8
+"""
+for i in range(4, 8, 2):
+    print(i)
+"""
+
 While loops go until a condition is no longer met.
 prints:
     0
@@ -355,11 +448,18 @@ try:
     # Use "raise" to raise an error
     raise IndexError("This is an index error")
 except IndexError as e:
-    pass    # Pass is just a no-op. Usually you would do recovery here.
+    pass                 # Pass is just a no-op. Usually you would do recovery here.
 except (TypeError, NameError):
-    pass    # Multiple exceptions can be handled together, if required.
-else:   # Optional clause to the try/except block. Must follow all except blocks
+    pass                 # Multiple exceptions can be handled together, if required.
+else:                    # Optional clause to the try/except block. Must follow all except blocks
     print("All good!")   # Runs only if the code in try raises no exceptions
+finally:                 #  Execute under all circumstances
+    print("We can clean up resources here")
+
+# Instead of try/finally to cleanup resources you can use a with statement
+with open("myfile.txt") as f:
+    for line in f:
+        print(line)
 
 # Python offers a fundamental abstraction called the Iterable.
 # An iterable is an object that can be treated as a sequence.
@@ -367,11 +467,11 @@ else:   # Optional clause to the try/except block. Must follow all except blocks
 
 filled_dict = {"one": 1, "two": 2, "three": 3}
 our_iterable = filled_dict.keys()
-print(our_iterable) #=> range(1,10). This is an object that implements our Iterable interface
+print(our_iterable)  # => dict_keys(['one', 'two', 'three']). This is an object that implements our Iterable interface.
 
 # We can loop over it.
 for i in our_iterable:
-    print(i)    # Prints one, two, three
+    print(i)  # Prints one, two, three
 
 # However we cannot address elements by index.
 our_iterable[1]  # Raises a TypeError
@@ -380,19 +480,18 @@ our_iterable[1]  # Raises a TypeError
 our_iterator = iter(our_iterable)
 
 # Our iterator is an object that can remember the state as we traverse through it.
-# We get the next object by calling the __next__ function.
-our_iterator.__next__()  #=> "one"
+# We get the next object with "next()".
+next(our_iterator)  # => "one"
 
-# It maintains state as we call __next__.
-our_iterator.__next__()  #=> "two"
-our_iterator.__next__()  #=> "three"
+# It maintains state as we iterate.
+next(our_iterator)  # => "two"
+next(our_iterator)  # => "three"
 
 # After the iterator has returned all of its data, it gives you a StopIterator Exception
-our_iterator.__next__() # Raises StopIteration
+next(our_iterator)  # Raises StopIteration
 
 # You can grab all the elements of an iterator by calling list() on it.
-list(filled_dict.keys())  #=> Returns ["one", "two", "three"]
-
+list(filled_dict.keys())  # => Returns ["one", "two", "three"]
 
 
 ####################################################
@@ -402,22 +501,20 @@ list(filled_dict.keys())  #=> Returns ["one", "two", "three"]
 # Use "def" to create new functions
 def add(x, y):
     print("x is {} and y is {}".format(x, y))
-    return x + y    # Return values with a return statement
+    return x + y  # Return values with a return statement
 
 # Calling functions with parameters
-add(5, 6)   # => prints out "x is 5 and y is 6" and returns 11
+add(5, 6)  # => prints out "x is 5 and y is 6" and returns 11
 
 # Another way to call functions is with keyword arguments
-add(y=6, x=5)   # Keyword arguments can arrive in any order.
-
+add(y=6, x=5)  # Keyword arguments can arrive in any order.
 
 # You can define functions that take a variable number of
 # positional arguments
 def varargs(*args):
     return args
 
-varargs(1, 2, 3)   # => (1, 2, 3)
-
+varargs(1, 2, 3)  # => (1, 2, 3)
 
 # You can define functions that take a variable number of
 # keyword arguments, as well
@@ -425,7 +522,7 @@ def keyword_args(**kwargs):
     return kwargs
 
 # Let's call it to see what happens
-keyword_args(big="foot", loch="ness")   # => {"big": "foot", "loch": "ness"}
+keyword_args(big="foot", loch="ness")  # => {"big": "foot", "loch": "ness"}
 
 
 # You can do both at once, if you like
@@ -442,27 +539,36 @@ all_the_args(1, 2, a=3, b=4) prints:
 # Use * to expand tuples and use ** to expand kwargs.
 args = (1, 2, 3, 4)
 kwargs = {"a": 3, "b": 4}
-all_the_args(*args)   # equivalent to foo(1, 2, 3, 4)
-all_the_args(**kwargs)   # equivalent to foo(a=3, b=4)
-all_the_args(*args, **kwargs)   # equivalent to foo(1, 2, 3, 4, a=3, b=4)
+all_the_args(*args)            # equivalent to foo(1, 2, 3, 4)
+all_the_args(**kwargs)         # equivalent to foo(a=3, b=4)
+all_the_args(*args, **kwargs)  # equivalent to foo(1, 2, 3, 4, a=3, b=4)
+
+# Returning multiple values (with tuple assignments)
+def swap(x, y):
+    return y, x  # Return multiple values as a tuple without the parenthesis.
+                 # (Note: parenthesis have been excluded but can be included)
 
+x = 1
+y = 2
+x, y = swap(x, y)     # => x = 2, y = 1
+# (x, y) = swap(x,y)  # Again parenthesis have been excluded but can be included.
 
-# Function Scope                                                                
+# Function Scope
 x = 5
 
-def setX(num):
+def set_x(num):
     # Local var x not the same as global variable x
-    x = num # => 43
-    print (x) # => 43
-    
-def setGlobalX(num):
+    x = num    # => 43
+    print (x)  # => 43
+
+def set_global_x(num):
     global x
-    print (x) # => 5
-    x = num # global var x is now set to 6
-    print (x) # => 6
+    print (x)  # => 5
+    x = num    # global var x is now set to 6
+    print (x)  # => 6
 
-setX(43)
-setGlobalX(6)
+set_x(43)
+set_global_x(6)
 
 
 # Python has first class functions
@@ -475,25 +581,28 @@ add_10 = create_adder(10)
 add_10(3)   # => 13
 
 # There are also anonymous functions
-(lambda x: x > 2)(3)   # => True
+(lambda x: x > 2)(3)                  # => True
+(lambda x, y: x ** 2 + y ** 2)(2, 1)  # => 5
 
 # TODO - Fix for iterables
 # There are built-in higher order functions
-map(add_10, [1, 2, 3])   # => [11, 12, 13]
-filter(lambda x: x > 5, [3, 4, 5, 6, 7])   # => [6, 7]
+map(add_10, [1, 2, 3])          # => [11, 12, 13]
+map(max, [1, 2, 3], [4, 2, 1])  # => [4, 2, 3]
+
+filter(lambda x: x > 5, [3, 4, 5, 6, 7])  # => [6, 7]
 
 # We can use list comprehensions for nice maps and filters
 # List comprehension stores the output as a list which can itself be a nested list
-[add_10(i) for i in [1, 2, 3]]  # => [11, 12, 13]
-[x for x in [3, 4, 5, 6, 7] if x > 5]   # => [6, 7]
+[add_10(i) for i in [1, 2, 3]]         # => [11, 12, 13]
+[x for x in [3, 4, 5, 6, 7] if x > 5]  # => [6, 7]
 
 ####################################################
 ## 5. Classes
 ####################################################
 
 
-# We subclass from object to get a class.
-class Human(object):
+# We use the "class" operator to get a class
+class Human:
 
     # A class attribute. It is shared by all instances of this class
     species = "H. sapiens"
@@ -501,11 +610,16 @@ class Human(object):
     # Basic initializer, this is called when this class is instantiated.
     # Note that the double leading and trailing underscores denote objects
     # or attributes that are used by python but that live in user-controlled
-    # namespaces. You should not invent such names on your own.
+    # namespaces. Methods(or objects or attributes) like: __init__, __str__,
+    # __repr__ etc. are called magic methods (or sometimes called dunder methods)
+    # You should not invent such names on your own.
     def __init__(self, name):
         # Assign the argument to the instance's name attribute
         self.name = name
 
+        # Initialize property
+        self.age = 0
+
     # An instance method. All methods take "self" as the first argument
     def say(self, msg):
         return "{name}: {message}".format(name=self.name, message=msg)
@@ -521,6 +635,23 @@ class Human(object):
     def grunt():
         return "*grunt*"
 
+    # A property is just like a getter.
+    # It turns the method age() into an read-only attribute
+    # of the same name.
+    @property
+    def age(self):
+        return self._age
+
+    # This allows the property to be set
+    @age.setter
+    def age(self, age):
+        self._age = age
+
+    # This allows the property to be deleted
+    @age.deleter
+    def age(self):
+        del self._age
+
 
 # Instantiate a class
 i = Human(name="Ian")
@@ -530,15 +661,26 @@ j = Human("Joel")
 print(j.say("hello"))  # prints out "Joel: hello"
 
 # Call our class method
-i.get_species()   # => "H. sapiens"
+i.get_species()  # => "H. sapiens"
 
 # Change the shared attribute
 Human.species = "H. neanderthalensis"
-i.get_species()   # => "H. neanderthalensis"
-j.get_species()   # => "H. neanderthalensis"
+i.get_species()  # => "H. neanderthalensis"
+j.get_species()  # => "H. neanderthalensis"
 
 # Call the static method
-Human.grunt()   # => "*grunt*"
+Human.grunt()    # => "*grunt*"
+
+# Update the property
+i.age = 42
+
+# Get the property
+i.age # => 42
+
+# Delete the property
+del i.age
+i.age  # => raises an AttributeError
+
 
 
 ####################################################
@@ -547,12 +689,12 @@ Human.grunt()   # => "*grunt*"
 
 # You can import modules
 import math
-print(math.sqrt(16))  # => 4
+print(math.sqrt(16))  # => 4.0
 
 # You can get specific functions from a module
 from math import ceil, floor
-print(ceil(3.7))  # => 4.0
-print(floor(3.7))   # => 3.0
+print(ceil(3.7))   # => 4.0
+print(floor(3.7))  # => 3.0
 
 # You can import all functions from a module.
 # Warning: this is not recommended
@@ -560,7 +702,7 @@ from math import *
 
 # You can shorten module names
 import math as m
-math.sqrt(16) == m.sqrt(16)   # => True
+math.sqrt(16) == m.sqrt(16)  # => True
 
 # Python modules are just ordinary python files. You
 # can write your own, and import them. The name of the
@@ -585,9 +727,7 @@ def double_numbers(iterable):
 # Instead of generating and returning all values at once it creates one in each
 # iteration.  This means values bigger than 15 wont be processed in
 # double_numbers.
-# Note range is a generator too. Creating a list 1-900000000 would take lot of
-# time to be made
-# We use a trailing underscore in variable names when we want to use a name that 
+# We use a trailing underscore in variable names when we want to use a name that
 # would normally collide with a python keyword
 range_ = range(1, 900000000)
 # will double all numbers until a result >=30 found
@@ -621,7 +761,7 @@ def say(say_please=False):
     return msg, say_please
 
 
-print(say())  # Can you buy me a beer?
+print(say())                 # Can you buy me a beer?
 print(say(say_please=True))  # Can you buy me a beer? Please! I am poor :(
 ```
 
@@ -629,18 +769,21 @@ print(say(say_please=True))  # Can you buy me a beer? Please! I am poor :(
 
 ### Free Online
 
+* [Automate the Boring Stuff with Python](https://automatetheboringstuff.com)
 * [Learn Python The Hard Way](http://learnpythonthehardway.org/book/)
 * [Dive Into Python](http://www.diveintopython.net/)
 * [Ideas for Python Projects](http://pythonpracticeprojects.com)
-
 * [The Official Docs](http://docs.python.org/3/)
 * [Hitchhiker's Guide to Python](http://docs.python-guide.org/en/latest/)
-* [Python Module of the Week](http://pymotw.com/3/)
 * [A Crash Course in Python for Scientists](http://nbviewer.ipython.org/5920182)
+* [Python Course](http://www.python-course.eu/index.php)
+* [First Steps With Python](https://realpython.com/learn/python-first-steps/)
+* [A curated list of awesome Python frameworks, libraries and software](https://github.com/vinta/awesome-python)
+* [30 Python Language Features and Tricks You May Not Know About](http://sahandsaba.com/thirty-python-language-features-and-tricks-you-may-not-know.html)
+* [Official Style Guide for Python](https://www.python.org/dev/peps/pep-0008/)
 
 ### Dead Tree
 
 * [Programming Python](http://www.amazon.com/gp/product/0596158106/ref=as_li_qf_sp_asin_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596158106&linkCode=as2&tag=homebits04-20)
 * [Dive Into Python](http://www.amazon.com/gp/product/1441413022/ref=as_li_tf_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=1441413022&linkCode=as2&tag=homebits04-20)
 * [Python Essential Reference](http://www.amazon.com/gp/product/0672329786/ref=as_li_tf_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0672329786&linkCode=as2&tag=homebits04-20)
-