diff options
Diffstat (limited to 'python3.html.markdown')
| -rw-r--r-- | python3.html.markdown | 86 |
1 files changed, 77 insertions, 9 deletions
diff --git a/python3.html.markdown b/python3.html.markdown index a1125c73..ea29fdba 100644 --- a/python3.html.markdown +++ b/python3.html.markdown @@ -5,6 +5,7 @@ contributors: - ["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 --- @@ -96,13 +97,13 @@ 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 +# (is vs. ==) is checks if two variables 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 = [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 @@ -173,6 +174,10 @@ some_var # => 5 # See Control Flow to learn more about exception handling. some_unknown_var # Raises a NameError +# 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 @@ -216,6 +221,17 @@ 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] +# 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 matching the argument +li.index(2) # => 1 +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] @@ -249,6 +265,8 @@ tup[:2] # => (1, 2) # 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 +# 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 @@ -306,6 +324,11 @@ filled_dict.update({"four":4}) # => {"one": 1, "two": 2, "three": 3, "four": 4} # 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() @@ -332,6 +355,15 @@ filled_set | other_set # => {1, 2, 3, 4, 5, 6} # Do set difference with - {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 @@ -397,7 +429,6 @@ 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) @@ -439,7 +470,7 @@ with open("myfile.txt") as f: 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: @@ -528,19 +559,19 @@ x, y = swap(x, y) # => x = 2, y = 1 # 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): +def set_global_x(num): global x 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 @@ -589,6 +620,9 @@ class Human: # 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) @@ -604,6 +638,23 @@ class Human: 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") @@ -623,6 +674,17 @@ j.get_species() # => "H. neanderthalensis" # Call the static method 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 + + #################################################### ## 6. Modules @@ -630,7 +692,7 @@ 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 @@ -654,6 +716,11 @@ math.sqrt(16) == m.sqrt(16) # => True import math dir(math) +# If you have a Python script named math.py in the same +# folder as your current script, the file math.py will +# be loaded instead of the built-in Python module. +# This happens because the local folder has priority +# over Python's built-in libraries. #################################################### ## 7. Advanced @@ -722,6 +789,7 @@ print(say(say_please=True)) # Can you buy me a beer? Please! I am poor :( * [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/) +* [Python 3 Computer Science Circles](http://cscircles.cemc.uwaterloo.ca/) ### Dead Tree |