Python 基本数据类型

基本数据类型：

Numbers：

        包含 Int 和 float 　　　　

x =3 
print(x)  # result: 3
x = 3.14
print(x)  # result: 3.14

 

　　加减乘除：

a = 6.28
print(a+1) # result: 6.28
print(a-5) # result: 1.2800000000000002 小数的精度问题，在这里不做赘述
print(a*2) # result: 12.56
print(a/2) # result: 3.14
b=3
print(b**3) # result: 27 

c=5
c +=1
print (c)  #result:6

Python 不支持c++或者c--的操作

Booleans:Python 支持所有的逻辑操作，但是python语言直接用英文单纯而不是&&或者||的符号

t = True
f = False
print(type(t)) # Prints "<class '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"

Strings:Python特别好的支持string类型

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"

      另外String对象还有很多有用的方法

s = "hello"
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"

容器：lists, dictionaries, sets 和tuples

Lists：list 相当于数组，但是他是被序列号的，可以包括不同数据类型的集合

x = [3,2,6]
print(x,x[2])   #result: print
print(x[-1])    # = x[2] index从后往前 result: 6
x[2]='foo'      # list 可以包括不能数据类似的值
print(x)        # result: [3, 2, 'foo']
x.append('bar') # list后面追加新元素
print(x)        # result: [3, 2, 'foo']
x1= x.pop()     # 从x list中出栈，指赋给x1
print(x,x1)     # result  [3, 2, 'foo'] bar

Slicing：切片

nums = list(range(5))   # range() 函数创建一个 int list
print(nums)             # result: [0, 1, 2, 3, 4]
print(nums[2:4])        # result: [2, 3] 返回一个切片从 index 2 to 4 但不包含4
print(nums[2:])         # result: [2, 3, 4] 返回一个切片从 index 2 to end
print(nums[:2])         # result: [0, 1] 返回一个切片从 index 0 to index, 但不包含index 本身
print(nums[:])          # result: [0, 1, 2, 3, 4] 返回全部
print(nums[:-1])        # result: [0, 1, 2, 3] 返回全部最后一个，不包含
nums[2:4]=[8,9]         # 分别赋值一个切片从 index 2 to 4 但不包含4
print(nums)             # result: [0, 1, 8, 9, 4]

Loops: 

animals = ['cat','dog','monkey']
for animal in animals:
    print(animal)
    # Prints "cat", "dog", "monkey"

可以用enumerate 函数遍历出元素的位置。

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

List comprehensions： 

nums = [0,1,2,3,4,5]
squares =[]
for x in nums:
    squares.append(x**2)
print(squares)# result:[0, 1, 4, 9, 16, 25]

你可以用 list comprehensions 实现

nums = [0,1,2,3,4,5]
squares =[x**2 for  x in nums]
print(squares) # result: [0, 1, 4, 9, 16, 25]

list comprehensions也可以加一些条件

nums = [0,1,2,3,4,5]
squares =[x**2 for  x in nums if x % 2 == 0]
print(squares) # result: [0, 4, 16]

Dictionaries

Dictionary 储存（key,value）对，类似java的的map，js中的object

d = {'cat':'cute','dog':'furry'}
print(d['cat']) # result: cute
print('cat' in d) # 检查 元素是否包含在dic内，结果只能是true false
d['fish'] = 'wet'
#print(d['sleep']) # key error 'sleep' not a key of d
print(d.get('sleep','N/A')) # 拿到一个key为sleep default value 是N/A
print(d.get('fish','N/A')) # 拿到一个key为fish default value 是N/A,如果value,显示，所以结果‘wet’
del d['fish']   # 删除一个元素
print(d.get('fish','N/A'))

Loops：

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

如果要进入dics 中的key和value 分别值，用items

d = {'person':2,'cat':4,'spider':8}
for animal,legs in d.items():
    print('A %s has %d legs' % (animal,legs))
# Prints "A person has 2 legs", "A cat has 4 legs", "A spider has 8 legs"

Dictionary comprehensions:

d = {'person':2,'cat':4,'spider':8}
#square = {k:v for (k,v)) in d.items()}
dict1_keys = {k*2:v**2 for (k,v) in d.items()}
print(dict1_keys)
{'personperson': 4, 'catcat': 16, 'spiderspider': 64}　　

Sets

一个无序的不同元素的集合

animals = {'cat','dog'}
print('cat' in animals)   # 查看元素是否在集合中 True, False
print('fish' in animals) # False
animals.add('fish')
print('fish' in animals) # Ture
print(len(animals))   # 3
animals.add('cat')   # 增加一个已经存在的元素对集合没有影响
print(len(animals))   #3
animals.remove('cat') 
print(len(animals))   #2

Loops：从下面结果就可以清楚了看出sets是无序的

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

Set comprehensions

animals = {'cat','dog','fish'}
a = {animal*2 for animal in animals}
print(a)
#{'fishfish', 'catcat', 'dogdog'}

Tuples:tuple 是可以认为一个有序的list，用法基本和List一样，一个不一样的地方是：tuple能像dict一样用key使用

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