基本参考于standford大学cs231n课程笔记cs231n-python numpy tutorial
略有删减与补充,欢迎交流指正

这一部分主要介绍python基本数据类型，学习过python基本语法的可不用看了

基本数据类型

1. 数字与数学运算

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"
x *= 2
print x  # Prints "8"
#注意！！！ python中无x++ x--
y = 2.5
print type(y) # Prints "<type 'float'>"
print y, y + 1, y * 2, y ** 2 # Prints "2.5 3.5 5.0 6.25"

2. 布尔型数据

t = True
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"
print t != f  # Logical XOR; prints "True"

3. 字符串

3.1 字符串的基本操作

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 formatting
print hw12  # prints "hello world 12"

3.2 字符串操作相关的函数

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; prints "  hello"
print s.center(7)     # Center a string, padding with spaces; prints " hello "
print s.replace('l', '(ell)')  # Replace all instances of one substring with another;
                               # prints "he(ell)(ell)o"
print '  world '.strip()  # Strip leading and trailing whitespace; prints "world"

复合数据类型

4. 列表

列表就是Python中的数组，但是列表长度可变，且能包含不同类型元素
4.1 列表的创建与索引

xs = [3, 1, 2]   # Create a list
print xs, xs[2]  # Prints "[3, 1, 2] 2"
print xs[-1]     # Negative indices count from the end of the list; prints "2"
xs[2] = 'foo'    # Lists can contain elements of different types
print xs         # Prints "[3, 1, 'foo']"
xs.append('bar') # Add a new element to the end of the list
print xs         # Prints 
x = xs.pop()     # Remove and return the last element of the list
print x, xs      # Prints "bar [3, 1, 'foo']"

4.2 对列表进行切片操作

nums = range(5)    # range is a built-in function that creates a list of integers
print nums         # Prints "[0, 1, 2, 3, 4]"
print nums[2:4]    # Get a slice from index 2 to 4 (exclusive); prints "[2, 3]"
print nums[2:]     # Get a slice from index 2 to the end; prints "[2, 3, 4]"
print nums[:2]     # Get a slice from the start to index 2 (exclusive); prints "[0, 1]"
print nums[:]      # Get a slice of the whole list; prints ["0, 1, 2, 3, 4]"
print nums[:-1]    # Slice indices can be negative; prints ["0, 1, 2, 3]"
nums[2:4] = [8, 9] # Assign a new sublist to a slice
print nums         # Prints "[0, 1, 8, 8, 4]"

4.3 循环

#循环
countries = ['China','America','Japan']
for country in countries:
    print country 
    '''
        China
        America
        Japan
    '''
for idx,country in enumerate(countries):
    print '%d:%s' %(idx+1,country)
    '''
        1:China
        2:America
        3:Japan
    '''

4.4 使用用列表推导式


#使用列表推导
nums = range(5) #[0,1,2,3,4]
squares = [a**2 for a in nums]
print squares #[0, 1, 4, 9, 16]
#添加条件的列表推导
nums = range(5)
even_squares = [a**2 for a in nums if(a%2==0)]
print even_squares #[0, 4, 16]

5. 字典

字典用来储存（键, 值）对，跟java里面的map（key,value）差不多
5.1 字典的基本操作

d = {'cat': 'cute', 'dog': 'furry'}  # Create a new dictionary with some data
print d['cat']       # Get an entry from a dictionary; prints "cute"
print 'cat' in d     # Check if a dictionary has a given key; prints "True"
d['fish'] = 'wet'    # Set an entry in a dictionary
print d['fish']      # Prints "wet"
# print d['monkey']  # KeyError: 'monkey' not a key of d
print d.get('monkey', 'N/A')  # Get an element with a default; prints "N/A" 
#防止keyerror错误 很重要的技巧
print d.get('fish', 'N/A')    # Get an element with a default; prints "wet"
del d['fish']        # Remove an element from a dictionary
print d.get('fish', 'N/A') # "fish" is no longer a key; prints "N/A"

5.2 字典循环

只访问键

d = {'person':2,'cat':4,'apider':8}
for animal in d:
    print 'A %s has %d legs' %(animal,d[animal])

访问键和值

for animal,legs in d.iteritems():
    print 'A %s has %d legs' %(animal,legs)
    '''
    A person has 2 legs
    A apider has 8 legs
    A cat has 4 legs
    '''

5.3 使用字典推导式

nums = range(5)
y = {x:x**2 for x in nums if x%2==0}#{0: 0, 2: 4, 4: 16}

6. 集合

集合是不同个体的无序集合
6.1 集合的基本操作

animals = {'cat', 'dog'}
print 'cat' in animals   # Check if an element is in a set; prints "True"
print 'fish' in animals  # prints "False"
animals.add('fish')      # Add an element to a set
print 'fish' in animals  # Prints "True"
print len(animals)       # Number of elements in a set; prints "3"
animals.add('cat')       # Adding an element that is already in the set does nothing
print len(animals)       # Prints "3"
animals.remove('cat')    # Remove an element from a set
print len(animals)       # Prints "2"

6.2 集合中的循环

animals = {'cat', 'dog', 'fish'}
for idx, animal in enumerate(animals):
    print '#%d: %s' % (idx + 1, animal)
# Prints "#1: fish", "#2: dog", "#3: cat"

6.3 使用集合推导式

from math import sqrt
nums = {int(sqrt(x)) for x in range(30)}
print nums  # Prints "set([0, 1, 2, 3, 4, 5])"

7. 元组

与列表类似不同的是元组中的值不可改变，元祖可以在字典中用作键，可以作为集合的元素，列表不行

d = {(x,x+1): x for x in range(10)}
print d #{(0, 1): 0, (1, 2): 1, (6, 7): 6, (5, 6): 5, (7, 8): 7, (8, 9): 8, (4, 5): 4, (2, 3): 2, (9, 10): 9, (3, 4): 3}
t = (5,6) #creat a tuple
print type(t) #<type 'tuple'>
print d[t] #5
print d[(1,2)] #1

8. 函数

python使用def创建函数，很简单，如下

def sign(x):
    if x > 0:
        return 'positive'
    elif x < 0:
        return 'negative'
    else:
        return 'zero'

for x in [-1, 0, 1]:
    print sign(x)
# Prints "negative", "zero", "positive"

带关键字参数的函数，下列中第二个参数为关键字参数，也称可选参数

def hello(name, loud=False):
    if loud:
        print 'HELLO, %s' % name.upper()
    else:
        print 'Hello, %s!' % name

hello('Bob') # Prints "Hello, Bob"
hello('Fred', loud=True)  # Prints "HELLO, FRED!"

9. 类

class Greeter(object):
    #构造函数
    def __init__(self,name):
        self.name = name
    #实例方法
    def greet(self,loud=False):
        if loud:
            print 'HELLO,%s' %self.name.upper()
        else:
            print 'Hello,%s' %self.name
g = Greeter('Fred')  # Construct an instance of the Greeter class
g.greet()            # Call an instance method; prints "Hello, Fred"
g.greet(loud=True)   # Call an instance method; prints "HELLO, FRED!"

numpy入门教程（一）