[Python基础]002.语法(1)

语法(1)

变量
基本数据类型
- 空值
- 布尔值
- 数字
- 字符串
- 列表
- 元组
- 字典
结构嵌套

变量

定义变量

i = 10

这样就定义了一个名为 i 的变量，它的值是 10 。

变量名必须是大小写英文、数字和_的组合，且不能用数字开头。
变量类型不需要指定，可以赋值任意数据类型。

多重赋值

a = b = c = 10 变量 a，b，c 都赋值为 10
a, b, c = 1, 2, 3 变量 a，b，c 分别赋值为 1，2，3

基本数据类型

空值

None 表示一个空对象，空值是Python里一个特殊的值，用None表示。

布尔值

真 True
假 False

数字

整数 i = 10
浮点数 f = 1.23 或 f = 1.23e-2
复数 c = 1 + 2j

数字计算

i = 10

j = 20.1

k = i + j

字符串 str

单引号 s = 'abc'
双引号 s = "abc" 与单引号一样。
在内容里有单引号时使用双引号，如s = "b = '单引号' "，反之亦然。
三引号

  s = '''abc

      Hello SD.Team

      It's Python strings

      '''

多行字符串，可以在里面任意使用单引号和双引号。

常用操作

s = 'abcdefg'

str[i] 取某个字符，0表示第一个字符

  print s[1]          # 返回'b'

  print s[-1]         # 取最后一个字符 返回'g'

str[i:j] 取一段字符

  print s[2:4]        # 取2到4 返回'cde'

  print s[2:]         # 取2到最后 返回'cdefg'

str1 + str2 组合字符串

  print s + 'hijk'    # 返回'abcdefghijk'

str * n 字符串复制

  print s * 2         # 返回'abcdefgabcdefg'

列表 list

就是数组，用中括号[ ] 定义，用逗号, 分割每项

sd_members = ['AC', 'Mount', 'Horse']

常用方法

len(list) 列表长度
```
  print len(sd_members)       # 返回3
```

list[i] 取某一项 i 取值范围 0~len(list)

  print sd_members[0]         # 取第一项 返回'AC'

  print sd_members[-1]        # 取倒数第一项 返回'Horse'

list[i:j] 取某一段

  print sd_members[0:2]       # 取前2项 返回['AC', 'Mount']

  print sd_members[1:]        # 从第一项取到最后一项 返回['Mount', 'Horse']

  print sd_members[:-1]       # 从第一项取到倒数第一项 返回['AC', 'Mount]

append(x) 添加项
```
  sd_members.append('Zergling')
```
del 删除某项
```
  del sd_members[0]
```

元组 tuple

不可变数组，内容不可修改，用括号( ) 定义，用逗号, 分割每项

sd_members = ('AC', 'Mount', 'Horse')

常用方法

len(tuple) 元组长度
```
  print len(sd_members)       #返回3
```

tuple[i] 取某一项 i 取值范围 -(len(list)) ~ len(list)-1

  print sd_members[0]         # 取第一项 返回'AC'

  print sd_members[-1]        # 取倒数第一项 返回'Horse'

tuple[i:j] 取某一段

  print sd_members[0:2]       # 取前2项 返回('AC', 'Mount')

  print sd_members[1:]        # 从第一项取到最后一项 返回('Mount', 'Horse')

  print sd_members[:-1]       # 从第一项取到倒数第一项 返回('AC', 'Mount)

字典 dict

键值对(key-value)，键唯一，用大括号{ } 定义，用冒号: 表示键值，用逗号, 分割每项

sd_members = {'AC': 170, 'Horse': 100, 'Mount': 160}

常用方法

len(dict) 字典数量
```
  print len(sd_members)
```
dict[key] 取某一项
```
  print sd_members['AC']
```
dict[new_key] = value 添加项
```
  sd_members['Zergling'] = 140
```

dict.has_key(key) 检验是否有这个键存在

  print sd_members.has_key('AC')

  print sd_members.has_key('Other')

del 删除键值对
```
  del sd_members['AC']
```

dict.keys() 获得所有key，以数组返回

  print sd_members.keys()         # 返回['AC', 'Mount', 'Horse']

dict.values() 获得所有value，以数组返回

  print sd_members.values()       # 返回[170, 160, 100]

dict.items() 获得所有key-value，以数组返回

  print sd_members.items()        # 返回[('AC', 170), ('Mount', 160), ('Horse', 100)]

结构嵌套

列表、元组、字典都是序列，可以相互嵌套形成多重数组等复杂的数据结构。
如 [('AC', 170), ('Mount', 160), ('Horse', 100)]，就是一个数组，这个数组里的项是元组。

sd_members = [('AC', 170), ('Mount', 160), ('Horse', 100)]

print sd_members[2]             # 返回('Horse', 100)

print sd_members[1][1]          # 返回160

字典里嵌套

sd_members = {'AC': [180, 170], 'Horse': [160, 100], 'Mount': [170, 160]}

print ad_members['Horse']       # 返回[160, 100]

print ad_members['AC'][1]       # 返回170

序列里可以放任意类型数据

abc = {1: 'a', 'key': 35, 'sd': {'name': 'sd', 'testing': [1, 2, 3, 4, 5]}}

print abc['sd']['testing'][2]       # 返回3

本站文章为宝宝巴士 SD.Team原创，转载务必在明显处注明：（作者官方网站：宝宝巴士)
转载自【宝宝巴士SuperDo团队】 原文链接: http://www.cnblogs.com/superdo/p/4494426.html

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