前言
本教程綜合Stanford CS231N和UC Berkerley CS188的Python教程。
教程很短，但適合有一定編程基礎，學過其他語言的童鞋。
Python
啓動Python 解釋器
Python可以有兩種使用方式，一種就是使用解釋器interpreter，類似Matlab，輸入一行代碼，運行一行；另一種就是編寫一個py後綴的文檔，稱爲腳本，然後python xxx.py運行腳本script。這裏我們使用解釋器。
在已安裝Python的情況下，在Terminal輸入python，可以啓動Python：
FloodSurges-MacBook-Pro:~ FloodSurge$ python
Python 2.7.9 (v2.7.9:648dcafa7e5f, Dec 10 2014, 10:10:46)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 這裏我是使用2.7.9版本的Python
操作符
在Python解釋器中，使用>>>來表示一行代碼，類似Matlab（使用<<）
先是最基本的操作符+，-，*，/：
>>> 1 + 1
2
>>> 2 * 3
6
>>> 2 / 3
0
>>> 2 / 3.1
0.6451612903225806接下來還有常用的次方運算，採用**
>>> 2 ** 2
4
>>> 2 ** 3
8數據類型
Python和其他語言很大的不同就是Python不需要定義數據類型，數據類型是根據數據的情況自行確定的。
比如上面的運算，輸入3就是整型，輸入3.1就是浮點數
數字
x=3

print type(x) # Prints "<type 'int'>"
print x # Prints "3"
print x + 1 # Addition; prints "4"
print x - 1 # Subtraction; prints "2"
print x * 2 # Multiplication; prints "6"
print x ** 2 # Exponentiation; prints "9"
x += 1
print x # Prints "4"注意Python不支持x++或者x–的操作
布爾量Boolean
用True和False表示
f = False
print type(t) # Prints "<type 'bool'>"
print t and f # Logical AND; prints "False"
print t or f # Logical OR; prints "True"
print not t # Logical NOT; prints "False"這裏要注意Python中不使用&&， ||，！來表示與，或，非
而是直接使用英語and，or，not
>>> 1==0
False
>>> not (1==0)
True
>>> (2==2) and (2==3)
False
>>> (2==2) or (2==3)
True字符串
hello = 'hello' # String literals can use single quotes
world = "world" # or double quotes; it does not matter.
print hello # Prints "hello"
print len(hello) # String length; prints "5"
hw = hello + ' ' + world # String concatenation
print hw # prints "hello world"
hw12 = '%s %s %d' % (hello, world, 12) # sprintf style string format
in
print hw12 # prints "hello world 12有很多現成的方法對字符串進行操作：

print s.capitalize() # Capitalize a string; prints "Hello"
print s.upper() # Convert a string to uppercase; prints "HELLO"
print s.rjust(7) # Right-justify a string, padding with spaces;
print s.center(7) # Center a string, padding with spaces; prints
print s.replace('l', '(ell)') # Replace all instances of one substri
# prints "he(ell)(ell)o">>> 'artificial' + "intelligence"
'artificialintelligence'事實上，不管是用單引號還是雙引號都是一樣的。
>>> a = 'hello'
>>> a
'hello'
>>> b = "hello"
>>> b
'hello'
>>> a == b
True那麼，我們可以通過dir和help來查看某個類型對應的methods.
>>> a = 'hello'
>>> dir(a)
['__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']
>>> help(a.find)
Help on built-in function find:
find(...)
S.find(sub [,start [,end]]) -> int
Return the lowest index in S where substring sub is found,
such that sub is contained within S[start:end]. Optional
arguments start and end are interpreted as in slice notation.
Return -1 on failure.上面的help之後按Q退出查看。
數據結構
List列表
>>> fruits = ['apple','orange','pear','banana']
>>> fruits[0]
'apple'可以通過 + 來連接列表
>>> otherFruits = ['kiwi','strawberry']
>>> fruits + otherFruits
>>> ['apple', 'orange', 'pear', 'banana', 'kiwi', 'strawberry']Python支持負值索引，比如fruits[-1]就是列表的最後一個。
>>> fruits[-2]
'pear'
>>> fruits.pop()
'banana'
>>> fruits
['apple', 'orange', 'pear']
>>> fruits.append('grapefruit')
>>> fruits
['apple', 'orange', 'pear', 'grapefruit']
>>> fruits[-1] = 'pineapple'
>>> fruits
['apple', 'orange', 'pear', 'pineapple']接下來可以用:來檢索多個數據：
>>> fruits[0:2]
['apple', 'orange']
>>> fruits[:3]
['apple', 'orange', 'pear']
>>> fruits[2:]
['pear', 'pineapple']
>>> len(fruits)
4然後lists也可以嵌套：
>>> lstOfLsts = [['a','b','c'],[1,2,3],['one','two','three']]
>>> lstOfLsts[1][2]
3
>>> lstOfLsts[0].pop()
'c'
>>> lstOfLsts
[['a', 'b'],[1, 2, 3],['one', 'two', 'three']]循環Loops：
animals = ['cat', 'dog', 'monkey']
for animal in animals:
 print animal
# Prints "cat", "dog", "monkey", each on its own line.如果要獲取每個元素的索引值，使用枚舉Enumerate：
animals = ['cat', 'dog', 'monkey']
for idx, animal in enumerate(animals):
 print '#%d: %s' % (idx + 1, animal)
# Prints "#1: cat", "#2: dog", "#3: monkey", each on its own lineList Comprehension 從一個數據轉換到另一個數據：
>>> nums = [0,1,2,3,4]
>>> squares = []
>>> for x in nums:
... squares.append(x ** 2)
...
>>> print squares
[0, 1, 4, 9, 16]也可以這麼寫：
>>> nums = [0,1,2,3,4]
>>> squares = [x**2 for x in nums]
>>> print squares
[0, 1, 4, 9, 16]還可以包含條件：
nums = [0, 1, 2, 3, 4]
even_squares = [x ** 2 for x in nums if x % 2 == 0]
print even_squares # Prints "[0, 4, 16]"Tuple
類似List，但初始化之後就不可更改
>>> pair = (3,5)
>>> pair[0]
3
>>> x,y = pair
>>> x
3
>>> y
5
>>> pair[1] = 6
TypeError: object does not support item assignmentSet集合
Set集合沒有順序
>>> shapes = ['circle','square','triangle','circle']
>>> setOfShapes = set(shapes)
>>> setOfShapes
set(['circle','square','triangle'])
>>> setOfShapes.add('polygon')
>>> setOfShapes
set(['circle','square','triangle','polygon'])
>>> 'circle' in setOfShapes
True
>>> 'rhombus' in setOfShapes
False
>>> favoriteShapes = ['circle','triangle','hexagon']
>>> setOfFavoriteShapes = set(favoriteShapes)
>>> setOfShapes - setOfFavoriteShapes
set(['square','polyon'])
>>> setOfShapes & setOfFavoriteShapes
set(['circle','triangle'])
>>> setOfShapes | setOfFavoriteShapes
set(['circle','square','triangle','polygon','hexagon'])Dictionary字典
類似java的Map，一個Key對應一個Value。
>>> studentIds = {'knuth': 42.0, 'turing': 56.0, 'nash': 92.0 }
>>> studentIds['turing']
56.0
>>> studentIds['nash'] = 'ninety-two'
>>> studentIds
{'knuth': 42.0, 'turing': 56.0, 'nash': 'ninety-two'}
>>> del studentIds['knuth']
>>> studentIds
{'turing': 56.0, 'nash': 'ninety-two'}
>>> studentIds['knuth'] = [42.0,'forty-two']
>>> studentIds
{'knuth': [42.0, 'forty-two'], 'turing': 56.0, 'nash': 'ninety-two'}
>>> studentIds.keys()
['knuth', 'turing', 'nash']
>>> studentIds.values()
[[42.0, 'forty-two'], 56.0, 'ninety-two']
>>> studentIds.items()
[('knuth',[42.0, 'forty-two']), ('turing',56.0), ('nash','ninety-two')]
>>> len(studentIds)
3寫腳本Script
就是新建一個文件，然後把後綴改成py。然後在裏面輸入代碼，比如foreach.py：
# This is what a comment looks like
fruits = ['apples','oranges','pears','bananas']
for fruit in fruits:
print fruit + ' for sale'
fruitPrices = {'apples': 2.00, 'oranges': 1.50, 'pears': 1.75}
for fruit, price in fruitPrices.items():
if price < 2.00:
print '%s cost %f a pound' % (fruit, price)
else:
print fruit + ' are too expensive!'然後在terminal在相應路徑下（記住不是在Python 解釋器下運行）
python foreach.py
apples for sale
oranges for sale
pears for sale
bananas for sale
oranges cost 1.500000 a pound
pears cost 1.750000 a pound
apples are too expensive!這裏還有兩個很有用的map和filter方法：
>>> map(lambda x: x * x, [1,2,3])
[1, 4, 9]
>>> filter(lambda x: x > 3, [1,2,3,4,5,4,3,2,1])
[4, 5, 4]注意空格
Python對語法要求很高，比如for語句下一個語句要空格否則可能報錯
>>> for x in nums:
... squares.append(x ** 2)
File "<stdin>", line 2
squares.append(x ** 2)
^
IndentationError: expected an indented block
>>> for x in nums:
... squares.append(x ** 2)Function函數
fruitPrices = {'apples':2.00, 'oranges': 1.50, 'pears': 1.75}
def buyFruit(fruit, numPounds):
if fruit not in fruitPrices:
print "Sorry we don't have %s" % (fruit)
else:
cost = fruitPrices[fruit] * numPounds
print "That'll be %f please" % (cost)
# Main Function
if __name__ == '__main__':
buyFruit('apples',2.4)
buyFruit('coconuts',2)Class 類
class FruitShop:
def __init__(self, name, fruitPrices):
"""
name: Name of the fruit shop
fruitPrices: Dictionary with keys as fruit
strings and prices for values e.g.
{'apples':2.00, 'oranges': 1.50, 'pears': 1.75}
"""
self.fruitPrices = fruitPrices
self.name = name
print 'Welcome to the %s fruit shop' % (name)
def getCostPerPound(self, fruit):
"""
fruit: Fruit string
Returns cost of 'fruit', assuming 'fruit'
is in our inventory or None otherwise
"""
if fruit not in self.fruitPrices:
print "Sorry we don't have %s" % (fruit)
return None
return self.fruitPrices[fruit]
def getPriceOfOrder(self, orderList):
"""
orderList: List of (fruit, numPounds) tuples
Returns cost of orderList. If any of the fruit are
"""
totalCost = 0.0
for fruit, numPounds in orderList:
costPerPound = self.getCostPerPound(fruit)
if costPerPound != None:
totalCost += numPounds * costPerPound
return totalCost
def getName(self):
return self.name使用對象Object
在前面在shop.py定義了FruitShop類，接下來我們可以在另外的腳本中使用這個類：
採用import
mport shop
shopName = 'the Berkeley Bowl'
fruitPrices = {'apples': 1.00, 'oranges': 1.50, 'pears': 1.75}
berkeleyShop = shop.FruitShop(shopName, fruitPrices)
applePrice = berkeleyShop.getCostPerPound('apples')
print applePrice
print('Apples cost $%.2f at %s.' % (applePrice, shopName))
otherName = 'the Stanford Mall'
otherFruitPrices = {'kiwis':6.00, 'apples': 4.50, 'peaches': 8.75}
otherFruitShop = shop.FruitShop(otherName, otherFruitPrices)
otherPrice = otherFruitShop.getCostPerPound('apples')
print otherPrice
print('Apples cost $%.2f at %s.' % (otherPrice, otherName))
print("My, that's expensive!")靜態和實例變量
在person_class.py中輸入：
class Person:
population = 0
def __init__(self, myAge):
self.age = myAge
Person.population += 1
def get_population(self):
return Person.population
def get_age(self):
return self.age這裏的population是一個靜態變量，或者說是全局變量
運行如下：
>>> import person_class
>>> p1 = person_class.Person(12)
>>> p1.get_population()
1
>>> p2 = person_class.Person(63)
>>> p1.get_population()
2
>>> p2.get_population()
2
>>> p1.get_age()
12
>>> p2.get_age()
63其他
使用range來循環：
for index in range(3):
print lst[index]