Andrew Schoen | @andrewschoen | @pythonkc
Python has a culture which finds an ideal balance between fast-moving innovation and diligent caution. It emphasizes readability, minimizes "magic," treats documentation as a first-class concern, [...] It blends approachability for beginners with maintainability for large projects, which has enabled its presence in fields as diverse as scientific computing, video games, systems automation, and the web.
Source: Heroku - Python and Django
dynamic and strongly typed
interpreted
whitespace is significant
multi-paradigm (OO, impertative, functional)
everything is an object
Created by Guido van Rossum in 1991
Is very diverse in it's usuage. Science, gaming, web and systems automation.
Has a very clearly-stated list of values
Development is driven through the use of PEPs (Python Enhancement Proposals)
The Zen of Python, by Tim Peters
Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than right now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!
$ python >>> 2 + 2 4 >>> 4 - 2 2 >>> 2 * 3 6 >>> 1 / 2 0 >>> 1.0 / 2 0.5 >>> 4 % 2 0 >>> 3 % 2 1
$ python >>> 4 4 >>> x Traceback (most recent call last): File "<stdin>", line 1, in <module> NameError: name 'x' is not defined >>> x = 4 >>> x 4
$ python >>> y = (1, 2, 3) >>> a, b, c = y >>> a 1 >>> b 2 >>> a = b = c = 1 >>> a, b, c (1, 1, 1)
$ python >>> "Hello" 'Hello' >>> name = "Andrew" >>> print "Hello " + name Hello Andrew
$ python
>>> print "Hello"
Hello
>>> print 'I'm a happy camper'
File "<stdin>", line 1
print 'I'm a happy camper'
^
SyntaxError: invalid syntax
>>> print "I'm a happy camper"
I'm a happy camper
$ python >>> "Hello " + 1 Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: cannot concatenate 'str' and 'int' objects >>> "Hello " * 2 'Hello Hello '
$ python
>>> print len('Hello')
5
>>> print len("")
0
>>> fish = "humuhumunukunukuapuaʻa"
>>> length = str(len(fish))
>>> print fish + " is a Hawaiian fish whose name is " + length + " characters long."
humuhumunukunukuapuaʻa is a Hawaiian fish whose name is 23 characters long.
$ python
>>> foo = "hello"
>>> bar = "world"
>>> "%s %s!!" % (foo, bar)
'hello world!!'
>>> foo + " " + bar
'hello world!!'
>>> "The answer is %d" % 42
'The answer is 42'
>>> ",".join((foo, bar))
'hello,world'
>>>>>> ",".join((foo, bar)).split(',')
['hello', 'world']
$ python
>>> x = ['one', 'two', 'three']
>>> x.append(4)
>>> x
['one', 'two', 'three', 4]
>>> x.remove('one')
>>> x
['two', 'three', 4]
>>> x.pop(1)
'three'
>>> x
['two', 4]
>>> x.insert(0, "one")
['one', 'two', 4]
$ python >>> x = ['one', 'two', 'three', 4] >>> x[1] 'two' >>> x[0:2] ['one', 'two'] >>> x[:-1] ['one', 'two', 'three'] >>> x[-1] 4 >>> x[0::2] ['one', 'three']
$ python >>> nums = [1, 2, 3, 4] >>> [x * 2 for x in nums] [2, 4, 6, 8] >>> [x for x in nums if x % 2 == 0] [2, 4]
$ python
>>> x = {}
>>> x
{}
>>> x = dict()
>>> x
{}
>>> x = {'hello':'world'}
>>> x
{'hello': 'world'}
$ python
>>> opposites = {'up':'down', 'left':'right'}
>>> opposites
{'up': 'down', 'left': 'right'}
>>> opposites['hot'] = 'cold'
>>> oposites
{'hot': 'cold', 'up': 'down', 'left': 'right'}
>>> del opposites['up']
>>> opposites
{'tall': 'short', 'hot': 'cold', 'left': 'right'}
>>> opposites['tall']
'short'
$ python
>>> opposites = {"up":"down", "left":"right"}
>>> opposites['dark']
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
KeyError: 'dark'
>>> opposites.get('dark', 'light')
'light'
$ python
>>> opposites = {"up":"down", "left":"right"}
>>> opposites.keys()
['up', 'left']
>>> opposites.values()
['down', 'right']
>>> ["The opposite of %s is %s" % (k, v) for
k, v in opposites.iteritems()]
['The opposite of up is down', 'The opposite of left is right']
$ python
>>> nums = (1, 2, 3)
>>> abcs = ('a', 'b', 'c')
>>> nums[1]
2
>>> # tuples can be nested
... nested = ('x', 'y', 'z'), nums, abcs
>>> nested
(('x', 'y', 'z'), (1, 2, 3), ('a', 'b', 'c'))
$ python >>> foo = (1, 2) >>> foo[0] = 3 Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'tuple' object does not support item assignment
$ python
>>> def add(x, y):
... return x + y
...
>>> add(2, 4)
6
>>> foo = (4, 6, add)
>>> foo[2](foo[0], foo[1])
10
>>> def bar(greeting, bangs=4):
... print "%s%s" % (greeting, "!" * bangs)
...
>>> bar("hello world", bangs=6)
hello world!!!!!!
$ python
>>> def foo(*args, **kwargs):
... for arg in args:
... print arg
... for k, v in kwargs.iteritems():
... print "%s=%s" % (k, v)
...
>>> foo("1", "2", key="value")
1
2
key=value
$ python
>>> def foo(name):
... def bar():
... return "Hello from %s" % name
... print bar()
...
>>> foo('Andrew')
Hello from Andrew
$ python >>> def f(x): ... return x*2 ... >>> f(3) 6 >>> times_two = lambda x: x*2 >>> times_two(3) 6 >>> (lambda x: x*2)(3) 6
$ python >>> class Person(object): ... def __init__(self, name="Andrew"): ... self.name = name ... def my_name(self): ... print "My name is %s" % self.name ... >>> kid = Person(name="Anderson") >>> kid.my_name() My name is Anderson >>> me = Person() >>> me.my_name() My name is Andrew
$ python >>> class Bar(object): ... def from_bar(self): ... print "from bar" >>> class Baz(object): ... def from_baz(self): ... print "from baz" >>> class Foo(Bar, Baz): ... def from_baz(self): ... print "overloaded!" >>> x = Foo() >>> x.from_bar() from bar >>> x.from_baz() overloaded!
$ python >>> if True: ... print "of course it is true" ... of course it is true >>> phrase = "hello world" >>> if "world" in phrase: ... print "hi world" ... hi world >>> if True and True: ... print "doubly true" ... doubly true
$ python >>> if True or False: ... print "half true" ... half true >>> phrase = "hello world" >>> if not phrase: ... print "no phrase" ... elif "hello world!!" == phrase: ... print "!!!" ... else: ... print phrase ... hello world
$ python
>>> for x in range(3):
... print x * 2
...
0
2
4
>>> opposites = {"up":"down","left":"right"}
>>> for k, v in opposites.items():
... print "The opposite of %s is %s" % (k, v)
...
The opposite of up is down
The opposite of left is right
$ python >>> abcs = "abc" >>> for index, char in enumerate(abcs): ... print index, char ... 0 a 1 b 2 c >>> for char in abcs: ... print char ... a b c
$ python >>> abcs = "abc" >>> for char in abcs: ... if "b" in char: ... continue ... print char ... a c >>> for char in abcs: ... if "b" in char: ... break ... print char ... a
$ python
>>> def reverse(data):
... for index in range(len(data)-1, -1, -1):
... yield data[index]
...
>>> reverse('Andy')
<generator object reverse at 0x1004992d0>
>>> for char in reverse('Andy'):
... print char
...
y
d
n
A
>>> nums = (i*i for i in range(10))
>>> sum(nums) # sum of squares
285
$ python >>> i = 0 >>> while i < 4: ... print i ... i += 1 ... 0 1 2 3
$ python >>> def divide(x, y): ... try: ... result = x / y ... except ZeroDivisionError, e: ... print "division by zero" ... else: ... print "result is %d" % result ... finally: ... print "should always print" ... >>> divide(2, 1) result is 2 should always print >>> divide(2, 0) division by zero should always print
$ python
>>> try:
... raise NameError("hello world")
... except NameError:
... print 'Got a NameError'
... raise
...
Got a NameError
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
NameError: hello world
$ python >>> x = [True, True, False] >>> any(x) True >>> all(x) False >>> dir(x) ['__add__', '__class__', '__contains__', '__delattr__', '__delitem__', '__delslice__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getslice__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__setslice__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']
$ python >>> x = "100" >>> int(x) 100 >>> y = 100 >>> str(y) '100' >>> len(x) 3 >>> type(y) <type 'int'>
$ python >>> nums = [1, 2, 3, 4] >>> map(lambda x: x*2, nums) [2, 4, 6, 8] >>> abcs = ['a','b','c','d'] >>> zip(nums, abcs) [(1, 'a'), (2, 'b'), (3, 'c'), (4, 'd')] >>> filter(lambda x: x % 2 == 0, nums) [2, 4] >>> max(nums) 4 >>> min(nums) 1
$ python >>> import random >>> movies = ["Star Wars", "Once", "Kung Fu Panda"] >>> random.choice(movies) 'Once'
$ python >>> class Person(object): ... def __init__(self, name="Andrew"): ... self.name=name ... def my_name(self): ... print "My name is %s" % self.name ... >>> me = Person() >>> hasattr(me, 'my_name') True >>> attr = getattr(me, 'my_name') >>> attr <bound method Person.my_name of <__main__.Person object at 0x10049cc50>> >>> attr() if callable(attr) else attr My name is Andrew
- http://docs.python.org
- http://learnpythonthehardway.org/
- http://diveintopython.net
- http://codingbat.com/python
- http://pythonchallenge.com
If you'd like to learn more about different projects in Python, check these out. Pip and virtualenv are a must for any Python dev.
@andrewschoen
@pythonkc