An (Inaccurate) Introduction to Python

•Easy to learn • Multi paradigm • Extensive library • Great community • Fun!

http://python.org/download/ (for now use the 2.7 version)

“Hello, World!” >>> print "Hello, World!"

“Hello, World!” $ python Python 2.6.1 (r261:67515, Jun 24 2010, 21:47:49) [GCC 4.2.1 (Apple Inc. build 5646)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> print "Hello, World!" Hello, World!

“Hello, World!” Start the Python interpreter $ python from the command line Python 2.6.1 (r261:67515, Jun 24 2010, 21:47:49) [GCC 4.2.1 (Apple Inc. build 5646)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> print "Hello, World!" Hello, World!

“Hello, World!” $ python Python 2.6.1 (r261:67515, Jun 24 2010, 21:47:49) [GCC 4.2.1 (Apple Inc. build 5646)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> print "Hello, World!" Hello, World! Generic information about the Python interpreter.

“Hello, World!” $ python Python 2.6.1 (r261:67515, Jun 24 2010, 21:47:49) [GCC 4.2.1 (Apple Inc. build 5646)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> print "Hello, World!" Hello, World! You type this bit...

“Hello, World!” $ python Python 2.6.1 (r261:67515, Jun 24 2010, 21:47:49) [GCC 4.2.1 (Apple Inc. build 5646)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> print "Hello, World!" Hello, World! Python returns the result (you made that happen!)

“Hello, World!” function def hello(name="World!"): """ Makes Python say hello. :param name: who to greet """ return "Hello, %s" % name

“Hello, World!” function Functions are named blocks of code that do stuff. def hello(name="World!"): """ Makes Python say hello. :param name: who to greet """ return "Hello, %s" % name

“Hello, World!” function def = deﬁne def hello(name="World!"): """ Makes Python say hello. :param name: who to greet """ return "Hello, %s" % name

“Hello, World!” function hello = name of function def hello(name="World!"): """ Makes Python say hello. :param name: who to greet """ return "Hello, %s" % name

“Hello, World!” function an argument (input) into the function def hello(name="World!"): """ Makes Python say hello. :param name: who to greet """ return "Hello, %s" % name

“Hello, World!” function a default value for the name arg def hello(name="World!"): """ Makes Python say hello. :param name: who to greet """ return "Hello, %s" % name

“Hello, World!” function def hello(name="World!"): """ Makes Python say hello. :param name: who to greet """ return "Hello, %s" % name Whitespace (a 4 space indent) indicates scope

“Hello, World!” function def hello(name="World!"): """ Makes Python say hello. comments & docs :param name: who to greet """ return "Hello, %s" % name

“Hello, World!” function def hello(name="World!"): """ Makes Python say hello. :param name: who to greet """ return "Hello, %s" % name return = result

“Hello, World!” function def hello(name="World!"): """ Makes Python say hello. :param name: who to greet """ return "Hello, %s" % name a string (use either ' or ")

“Hello, World!” function def hello(name="World!"): """ Makes Python say hello. :param name: who to greet """ return "Hello, %s" % name string formatting

Call the function (note the brackets) >>> hello() 'Hello, World!' >>> hello("NortHACKton") 'Hello, NortHACKton' >>> hello("Widget") 'Hello, Widget'

>>> hello() Here’s the result... 'Hello, World!' >>> hello("NortHACKton") 'Hello, NortHACKton' >>> hello("Widget") 'Hello, Widget'

>>> hello() 'Hello, World!' >>> hello("NortHACKton") 'Hello, NortHACKton' >>> hello("Widget") 'Hello, Widget' Aha! Pass in arguments between the brackets...

HELP! >>> dir() ['__builtins__', '__doc__', '__name__', '__package__', 'hello'] >>> help(hello) Help on function hello in module __main__: hello(name='World!') Makes Python say hello. :param name: who to greet

HELP! >>> dir() return the attributes of given scope ['__builtins__', '__doc__', '__name__', '__package__', 'hello'] >>> help(hello) display help from docstring Help on function hello in module __main__: hello(name='World!') Makes Python say hello. :param name: who to greet

Assignment >>> greeting = hello('NortHACKton!') >>> greeting 'Hello, NortHACKton!' >>> type(greeting) <type 'str'> >>> foo = 1 >>> type(foo) <type 'int'> >>> bar = 1.234 >>> type(bar) <type 'float'> >>> dir(greeting) ['__add__', '__class__', '__contains__', '__delattr__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__getslice__', '__gt__', '__hash__', '__init__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '_formatter_field_name_split', '_formatter_parser', 'capitalize', 'center', 'count', 'decode', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']

Assignment >>> greeting = hello('NortHACKton!') >>> greeting greeting holds the return value 'Hello, NortHACKton!' and it’s a string (of characters)! >>> type(greeting) <type 'str'> >>> foo = 1 >>> type(foo) <type 'int'> >>> bar = 1.234 >>> type(bar) <type 'float'> >>> dir(greeting) ['__add__', '__class__', '__contains__', '__delattr__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__getslice__', '__gt__', '__hash__', '__init__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '_formatter_field_name_split', '_formatter_parser', 'capitalize', 'center', 'count', 'decode', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']

Assignment >>> greeting = hello('NortHACKton!') >>> greeting 'Hello, NortHACKton!' >>> type(greeting) foo holds the number 1 <type 'str'> >>> foo = 1 >>> type(foo) <type 'int'> >>> bar = 1.234 and it’s an integer (whole number)! >>> type(bar) <type 'float'> >>> dir(greeting) ['__add__', '__class__', '__contains__', '__delattr__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__getslice__', '__gt__', '__hash__', '__init__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '_formatter_field_name_split', '_formatter_parser', 'capitalize', 'center', 'count', 'decode', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']

Assignment >>> greeting = hello('NortHACKton!') >>> greeting 'Hello, NortHACKton!' >>> type(greeting) <type 'str'> >>> foo = 1 >>> type(foo) bar holds the number 1.234 <type 'int'> >>> bar = 1.234 >>> type(bar) <type 'float'> >>> dir(greeting) and it’s a ﬂoat (’ing point number)! ['__add__', '__class__', '__contains__', '__delattr__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__getslice__', '__gt__', '__hash__', '__init__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '_formatter_field_name_split', '_formatter_parser', 'capitalize', 'center', 'count', 'decode', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']

Assignment >>> greeting = hello('NortHACKton!') >>> greeting 'Hello, NortHACKton!' >>> type(greeting) <type 'str'> >>> foo = 1 >>> type(foo) <type 'int'> >>> bar = 1.234 >>> type(bar) <type 'float'> >>> dir(greeting) remember this..? ['__add__', '__class__', '__contains__', '__delattr__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__getslice__', '__gt__', '__hash__', '__init__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '_formatter_field_name_split', '_formatter_parser', 'capitalize', 'center', 'count', 'decode', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']

Assignment >>> greeting = hello('NortHACKton!') >>> greeting 'Hello, NortHACKton!' >>> type(greeting) <type 'str'> >>> foo = 1 >>> type(foo) <type 'int'> >>> bar = 1.234 >>> type(bar) <type 'float'> >>> dir(greeting) ['__add__', '__class__', '__contains__', '__delattr__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__getslice__', '__gt__', '__hash__', '__init__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '_formatter_field_name_split', '_formatter_parser', 'capitalize', 'center', 'count', 'decode', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill'] All of the attributes/functions of “greeting”

Program ﬂow... >>> world_is_flat = False >>> if world_is_flat: ... print "The world is flat!" ... else: ... print "The world is round" ... The world is round

Program ﬂow... >>> world_is_flat = False >>> if world_is_flat: “if” tests for truth ... print "The world is flat!" ... else: “else” if “if” evaluates to false ... print "The world is round" ... The world is round The result of this logic...

Program ﬂow... >>> world_is_flat = False >>> if world_is_flat: ... print "The world is flat!" ... else: ... print "The world is round" ... The world is round NB: there is NO switch in Python. Use elif for further clauses in the logic.

Loops >>> for number in range(10): ... print number ... Basically, for each “something” in a group of “somethings” do something (for each number in a group of numbers print the number)

Loops >>> for number in range(10): ... print number ... 0 1 2 3 Like many programming languages, 4 Python starts counting from 0 (zero) 5 6 7 8 9 There’s also while

Data structures >>> my_dictionary = { curly brackets! ... 'key': 'value', ... 1: 2, dict = key/value store ... 'branch': { ... 'leaf': 'node' (think phone book) ... } ... } >>> my_dictionary['key'] get the value from the dict 'value' >>> my_dictionary[1] 2 >>> my_dictionary['branch']['leaf'] 'node' >>> my_dictionary {1: 2, 'branch': {'leaf': 'node'}, 'key': 'value'} Why not try dir(my_dictionary)and play.?

Data structures >>> shopping = ['eggs', 'ham', 'spam', 'parrot'] a list >>> len(shopping) 4 square brackets! >>> shopping ['eggs', 'ham', 'spam', 'parrot'] lists remain in order >>> shopping[0] 'eggs' >>> shopping[3] get a speciﬁc item by position 'parrot' >>> shopping[4] Traceback (most recent call last): start counting from File "<stdin>", line 1, in <module> IndexError: list index out of range zero (remember?) >>> shopping[1:] ['ham', 'spam', 'parrot'] >>> shopping[:1] ['eggs'] >>> shopping[:-1] slicing ['eggs', 'ham', 'spam'] >>> shopping[-1:] ['parrot']

Modules import antigravity from antigravity import stasisfield stasisfield.generate()

In a nutshell (there’s much more to it than this) Classes deﬁne sorts of things Objects are instances of classes

Cow = class Buttercup = object (an instance of cow)

In a nutshell (part 2) (there’s still much more to it than this) Methods do things (they’re functions) Attributes deﬁne, er, attributes...

Moo! Buttercup.moo() Buttercup.breed = “friesian”

A very simple view... Nouns = Classes Proper Nouns = Objects Verbs = Methods Adjectives = Attributes er, sort of... I’m making this up as I go along... :-)

class Cow(object): """ A pythonic cow """ def __init__(self, name="Cow", breed=None): """ Called when the class is instantiated """ self.name = name self.breed = breed def moo(self, message="MOO!"): """ A bovine hello world! """ return "%s says, %s" % (self.name, message)

Indicates we’re deﬁning a new class... class Cow(object): """ A pythonic cow """ def __init__(self, name="Cow", breed=None): """ Called when the class is instantiated """ self.name = name self.breed = breed def moo(self, message="MOO!"): """ A bovine hello world! """ return "%s says, %s" % (self.name, message)

... that we’re calling “Cow”... class Cow(object): """ A pythonic cow """ def __init__(self, name="Cow", breed=None): """ Called when the class is instantiated """ self.name = name self.breed = breed def moo(self, message="MOO!"): """ A bovine hello world! """ return "%s says, %s" % (self.name, message)

... that inherits attributes/behaviour from the“object” class. class Cow(object): """ A pythonic cow """ def __init__(self, name="Cow", breed=None): """ Called when the class is instantiated """ self.name = name self.breed = breed def moo(self, message="MOO!"): """ A bovine hello world! """ return "%s says, %s" % (self.name, message)

class Cow(object): A docstring that explains """ A pythonic cow what this class represents """ def __init__(self, name="Cow", breed=None): """ Called when the class is instantiated """ self.name = name self.breed = breed def moo(self, message="MOO!"): """ A bovine hello world! """ return "%s says, %s" % (self.name, message)

class Cow(object): """ A pythonic cow """ def __init__(self, name="Cow", breed=None): """ A special Called when the class is instantiated """ method self.name = name self.breed = breed called when a new def moo(self, message="MOO!"): """ object is A bovine hello world! """ created return "%s says, %s" % (self.name, message) with this class

class Cow(object): """ A pythonic cow “self” refers to the new """ object (e.g. Buttercup) def __init__(self, name="Cow", breed=None): """ Called when the class is instantiated """ self.name = name self.breed = breed def moo(self, message="MOO!"): """ A bovine hello world! """ return "%s says, %s" % (self.name, message)

class Cow(object): """ A pythonic cow """ def __init__(self, name="Cow", breed=None): """ Called when the class is instantiated """ self.name = name self.name and self.breed self.breed = breed are attributes of the def moo(self, message="MOO!"): instantiated object """ A bovine hello world! (Buttercup) """ return "%s says, %s" % (self.name, message)

class Cow(object): """ A pythonic cow """ def __init__(self, name="Cow", breed=None): """ Called when the class is instantiated """ self.name = name self.breed = breed def moo(self, message="MOO!"): """ A bovine hello world! A method """ return "%s says, %s" % (self.name, message) makes the object do something

>>> from example import Cow >>> buttercup = cow("Buttercup", "friesian") >>> buttercup.name 'Buttercup' >>> buttercup.breed 'friesian' >>> buttercup.moo() 'Buttercup says, MOO!'

http://docs.python.org/tutorial/introduction.html

and now for something completely different...

Your task: Create a Parrot class. It must be able to squawk, ﬂap and, ahem, become deceased. If the parrot is deceased then calling squawk and ﬂap return the message “This is an ex- parrot”. We should be able to indicate the parrot’s breed and give it a name. Use your imagination! HAVE FUN!

An (Inaccurate) Introduction to Python

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