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python数据类型详解及列表字典集合推导式详解

时间：2016-10-13 19:13:36      阅读：533      评论：0      收藏：0      [点我收藏+]

标签：

一.运算符

Python语言支持以下类型的运算符：

  • 算术运算符

技术分享

如：

#!/usr/bin/env python
# -*- coding:utf-8 -*-

a = 5
b = 6
print(a + b)

 

  • 比较运算符

技术分享

例：

#!/usr/bin/env python
# -*- coding:utf-8 -*-

a = 5
b = 6
if a < b:
    print(True)
else:
    print(False)

 

  • 赋值运算符

技术分享

例：

#!/usr/bin/env python
# -*- coding:utf-8 -*-

a = 5
b = a
print(b)

 

  • 逻辑运算符

技术分享

例：

#!/usr/bin/env python
# -*- coding:utf-8 -*-

a = 5
b = 6
if a >4 and b < 10:
    print(True)
else:
    print(False)

 

  • 成员运算符

技术分享

例：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
value = "a"
list = [‘a‘,‘b‘]

if value in list:
    print(True)

二.数据类型

  1. 数字

int(整形），数字数据类型用于存储数值

Python 支持三种不同的数值类型：

  • 整型(Int) - 通常被称为是整型或整数，是正或负整数，不带小数点。Python3 整型是没有限制大小的，可以当作 Long 类型使用，所以 Python3 没有 Python2 的 Long 类型。
  • 浮点型(float) - 浮点型由整数部分与小数部分组成，浮点型也可以使用科学计数法表示（2.5e2 = 2.5 x 102 = 250）
  • 复数- 复数由实数部分和虚数部分构成，可以用a + bj,或者complex(a,b)表示， 复数的实部a和虚部b都是浮点型
技术分享 
class int(object):
    """
    int(x=0) -> int or long
    int(x, base=10) -> int or long
    
    Convert a number or string to an integer, or return 0 if no arguments
    are given.  If x is floating point, the conversion truncates towards zero.
    If x is outside the integer range, the function returns a long instead.
    
    If x is not a number or if base is given, then x must be a string or
    Unicode object representing an integer literal in the given base.  The
    literal can be preceded by ‘+‘ or ‘-‘ and be surrounded by whitespace.
    The base defaults to 10.  Valid bases are 0 and 2-36.  Base 0 means to
    interpret the base from the string as an integer literal.
    >>> int(‘0b100‘, base=0)
    """
    def bit_length(self): 
        """ 返回表示该数字的时占用的最少位数 """
        """
        int.bit_length() -> int
        
        Number of bits necessary to represent self in binary.
        >>> bin(37)
        ‘0b100101‘
        >>> (37).bit_length()
        """
        return 0

    def conjugate(self, *args, **kwargs): # real signature unknown
        """ 返回该复数的共轭复数 """
        """ Returns self, the complex conjugate of any int. """
        pass

    def __abs__(self):
        """ 返回绝对值 """
        """ x.__abs__() <==> abs(x) """
        pass

    def __add__(self, y):
        """ x.__add__(y) <==> x+y """
        pass

    def __and__(self, y):
        """ x.__and__(y) <==> x&y """
        pass

    def __cmp__(self, y): 
        """ 比较两个数大小 """
        """ x.__cmp__(y) <==> cmp(x,y) """
        pass

    def __coerce__(self, y):
        """ 强制生成一个元组 """ 
        """ x.__coerce__(y) <==> coerce(x, y) """
        pass

    def __divmod__(self, y): 
        """ 相除，得到商和余数组成的元组 """ 
        """ x.__divmod__(y) <==> divmod(x, y) """
        pass

    def __div__(self, y): 
        """ x.__div__(y) <==> x/y """
        pass

    def __float__(self): 
        """ 转换为浮点类型 """ 
        """ x.__float__() <==> float(x) """
        pass

    def __floordiv__(self, y): 
        """ x.__floordiv__(y) <==> x//y """
        pass

    def __format__(self, *args, **kwargs): # real signature unknown
        pass

    def __getattribute__(self, name): 
        """ x.__getattribute__(‘name‘) <==> x.name """
        pass

    def __getnewargs__(self, *args, **kwargs): # real signature unknown
        """ 内部调用 __new__方法或创建对象时传入参数使用 """ 
        pass

    def __hash__(self): 
        """如果对象object为哈希表类型，返回对象object的哈希值。哈希值为整数。在字典查找中，哈希值用于快速比较字典的键。两个数值如果相等，则哈希值也相等。"""
        """ x.__hash__() <==> hash(x) """
        pass

    def __hex__(self): 
        """ 返回当前数的 十六进制 表示 """ 
        """ x.__hex__() <==> hex(x) """
        pass

    def __index__(self): 
        """ 用于切片，数字无意义 """
        """ x[y:z] <==> x[y.__index__():z.__index__()] """
        pass

    def __init__(self, x, base=10): # known special case of int.__init__
        """ 构造方法，执行 x = 123 或 x = int(10) 时，自动调用，暂时忽略 """ 
        """
        int(x=0) -> int or long
        int(x, base=10) -> int or long
        
        Convert a number or string to an integer, or return 0 if no arguments
        are given.  If x is floating point, the conversion truncates towards zero.
        If x is outside the integer range, the function returns a long instead.
        
        If x is not a number or if base is given, then x must be a string or
        Unicode object representing an integer literal in the given base.  The
        literal can be preceded by ‘+‘ or ‘-‘ and be surrounded by whitespace.
        The base defaults to 10.  Valid bases are 0 and 2-36.  Base 0 means to
        interpret the base from the string as an integer literal.
        >>> int(‘0b100‘, base=0)
        # (copied from class doc)
        """
        pass

    def __int__(self): 
        """ 转换为整数 """ 
        """ x.__int__() <==> int(x) """
        pass

    def __invert__(self): 
        """ x.__invert__() <==> ~x """
        pass

    def __long__(self): 
        """ 转换为长整数 """ 
        """ x.__long__() <==> long(x) """
        pass

    def __lshift__(self, y): 
        """ x.__lshift__(y) <==> x<<y """
        pass

    def __mod__(self, y): 
        """ x.__mod__(y) <==> x%y """
        pass

    def __mul__(self, y): 
        """ x.__mul__(y) <==> x*y """
        pass

    def __neg__(self): 
        """ x.__neg__() <==> -x """
        pass

    @staticmethod # known case of __new__
    def __new__(S, *more): 
        """ T.__new__(S, ...) -> a new object with type S, a subtype of T """
        pass

    def __nonzero__(self): 
        """ x.__nonzero__() <==> x != 0 """
        pass

    def __oct__(self): 
        """ 返回改值的 八进制 表示 """ 
        """ x.__oct__() <==> oct(x) """
        pass

    def __or__(self, y): 
        """ x.__or__(y) <==> x|y """
        pass

    def __pos__(self): 
        """ x.__pos__() <==> +x """
        pass

    def __pow__(self, y, z=None): 
        """ 幂，次方 """ 
        """ x.__pow__(y[, z]) <==> pow(x, y[, z]) """
        pass

    def __radd__(self, y): 
        """ x.__radd__(y) <==> y+x """
        pass

    def __rand__(self, y): 
        """ x.__rand__(y) <==> y&x """
        pass

    def __rdivmod__(self, y): 
        """ x.__rdivmod__(y) <==> divmod(y, x) """
        pass

    def __rdiv__(self, y): 
        """ x.__rdiv__(y) <==> y/x """
        pass

    def __repr__(self): 
        """转化为解释器可读取的形式 """
        """ x.__repr__() <==> repr(x) """
        pass

    def __str__(self): 
        """转换为人阅读的形式，如果没有适于人阅读的解释形式的话，则返回解释器课阅读的形式"""
        """ x.__str__() <==> str(x) """
        pass

    def __rfloordiv__(self, y): 
        """ x.__rfloordiv__(y) <==> y//x """
        pass

    def __rlshift__(self, y): 
        """ x.__rlshift__(y) <==> y<<x """
        pass

    def __rmod__(self, y): 
        """ x.__rmod__(y) <==> y%x """
        pass

    def __rmul__(self, y): 
        """ x.__rmul__(y) <==> y*x """
        pass

    def __ror__(self, y): 
        """ x.__ror__(y) <==> y|x """
        pass

    def __rpow__(self, x, z=None): 
        """ y.__rpow__(x[, z]) <==> pow(x, y[, z]) """
        pass

    def __rrshift__(self, y): 
        """ x.__rrshift__(y) <==> y>>x """
        pass

    def __rshift__(self, y): 
        """ x.__rshift__(y) <==> x>>y """
        pass

    def __rsub__(self, y): 
        """ x.__rsub__(y) <==> y-x """
        pass

    def __rtruediv__(self, y): 
        """ x.__rtruediv__(y) <==> y/x """
        pass

    def __rxor__(self, y): 
        """ x.__rxor__(y) <==> y^x """
        pass

    def __sub__(self, y): 
        """ x.__sub__(y) <==> x-y """
        pass

    def __truediv__(self, y): 
        """ x.__truediv__(y) <==> x/y """
        pass

    def __trunc__(self, *args, **kwargs): 
        """ 返回数值被截取为整形的值，在整形中无意义 """
        pass

    def __xor__(self, y): 
        """ x.__xor__(y) <==> x^y """
        pass

    denominator = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
    """ 分母 = 1 """
    """the denominator of a rational number in lowest terms"""

    imag = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
    """ 虚数，无意义 """
    """the imaginary part of a complex number"""

    numerator = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
    """ 分子 = 数字大小 """
    """the numerator of a rational number in lowest terms"""

    real = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
    """ 实属，无意义 """
    """the real part of a complex number"""

int
View Code

 

 

2.布尔值

真或者假，1或者0

 

3.字符串

字符串是python中最常见类型，我们通常用单引号(‘‘)或者双引号("")来创建

例：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
value = "a"
print(value)
字符串常用功能：
  • 移除空白

例;

#!/usr/bin/env python
# -*- coding:utf-8 -*-
value = " a "
ret = value.strip()
print(ret)

 

  • 分割

例：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
value = "hello,world"
ret = value.split(‘,‘)
print(ret)

 

  • 长度

例：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
value = "hello,world"
ret = value.__len__()
print(ret)

 

  • 索引

例：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
value = "hello,world"
ret = value[0]
print(ret)

 

  • 切片

例：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
value = "hello,world"
ret = value[0:6]
print(ret)

字符串内建函数

#!/usr/bin/env python
# -*- coding:utf-8 -*-
"""
capitalize()
将字符串的第一个字符转换为大写
"""
value = " hello,world "
ret = value.capitalize()
print(ret)
"""
center(width, fillchar)
返回一个指定的宽度 width 居中的字符串，fillchar 为填充的字符，默认为空格
"""
ret = value.center(30)
print(ret)

"""
count(str, beg= 0,end=len(string))
返回 str 在 string 里面出现的次数，如果 beg 或者 end 指定则返回指定范围内 str 出现的次数
"""
ret = value.count(‘l‘)
print(ret)
"""
decode(encoding=‘UTF-8‘,errors=‘strict‘)
使用指定编码来解码字符串。默认编码为字符串编码
encode(encoding=‘UTF-8‘,errors=‘strict‘)
以 encoding 指定的编码格式编码字符串

temp = "中文"
#解码，需要指定原来是什么编码
temp_unicode = temp.decode(‘utf-8‘)
#编码，需要指定要编成什么编码
temp_gbk = temp_unicode.encode(‘gbk‘)
print(temp_gbk)
"""
"""
endswith(suffix, beg=0, end=len(string))
检查字符串是否以某字符串结尾如果是，返回 True,否则返回 False.
"""
ret = value.endswith(‘d‘)
print(ret)
"""
expandtabs(tabsize=8)
把字符串 string 中的 tab 符号转为空格，tab 符号默认的空格数是 8
"""
ret = value.expandtabs()
print(ret)
"""
find(str, beg=0 end=len(string))
检测 str 是否包含在字符串中 中，则检查是否包含在指定范围内，如果是返回开始的索引值，否则返回-1
"""
ret = value.find(‘h‘)
print(ret)

"""
index(str, beg=0, end=len(string))
跟find()方法一样，只不过如果str不在字符串中会报一个异常,使用find方法最佳
"""
"""
isdigit()
如果字符串只包含数字则返回 True 否则返回 False
"""
ret = value.isdigit()
print(ret)

"""
lstrip()
截掉字符串左边的空格
"""
ret = value.lstrip()
print(ret)

"""
rstrip()
删除字符串字符串末尾的空格
"""
ret = value.rstrip()
print(ret)
"""
split(str="", num=string.count(str))
num=string.count(str)) 以 str 为分隔符截取字符串
"""
ret = value.split(‘,‘)
print(ret)

"""
strip([chars])
去除左右空格
"""
ret = value.strip()
print(ret)

"""
title()
返回"标题化"的字符串,就是说所有单词都是以大写开始，其余字母均为小写
"""
ret = value.title()
print(ret)

python字符串格式化符号:

技术分享

 

4.列表

列表中每个位置都分配一个数字，从0开始，依此类推

基本操作：

  • 索引
  • 切片
  • 追加
  • 删除
  • 长度
  • 循环
  • 包含

创建列表

#!/usr/bin/env python
# -*- coding:utf-8 -*-
list = [‘a‘,‘b‘]

例：

#!/usr/bin/env python
# -*- coding:utf-8 -*-
"""
索引
"""

list = [‘a‘,‘b‘]
ret = list[0]
print(ret)
　　切片
#!/usr/bin/env python
# -*- coding:utf-8 -*-
"""
切片
"""

list = [‘a‘,‘b‘,‘c‘]
ret = list[0:2]
print(ret)

　　追加

#!/usr/bin/env python
# -*- coding:utf-8 -*-
"""
追加
"""
list = [‘a‘,‘b‘,‘c‘]
list.append(‘d‘)
print(list)

删除

#!/usr/bin/env python
# -*- coding:utf-8 -*-
"""
删除索引1
"""

list = [‘a‘,‘b‘,‘c‘]
print(list)
del list[1]
print(list)

长度

#!/usr/bin/env python
# -*- coding:utf-8 -*-
list = [‘a‘,‘b‘,‘c‘]
ret=list.__len__()
print(ret)

　　循环

#!/usr/bin/env python
# -*- coding:utf-8 -*-
list = [‘a‘,‘b‘,‘c‘]

for i in list:
    print(i)

　　包含

#!/usr/bin/env python
# -*- coding:utf-8 -*-
list = [‘a‘,‘b‘,‘c‘]
list2 = [‘d‘,‘e‘]
total = [list + list2]
print(total)

列表中内置函数

#!/usr/bin/env python
# -*- coding:utf-8 -*-
"""
排序
"""
list = [1,4,2,3,4,5,10,3]
list.sort()
print(list)

"""
list.count(obj)
统计某个元素在列表中出现的次数
"""
ret = list.count(3)
print(ret)

"""
list.extend(seq)
在列表末尾一次性追加另一个序列中的多个值（用新列表扩展原来的列表）
"""
list2 = [100,101,105]
list.extend(list2)
print(list)

"""
list.pop(obj=list[-1])
移除列表中的一个元素（默认最后一个元素），并且返回该元素的值
"""
list.pop()
print(list)
"""
list.remove(obj)
移除列表中某个值的第一个匹配项
"""
list.remove(1)
print(list)
"""
list.reverse()
反向列表中元素
"""
list.reverse()
print(list)
"""
list.clear()
清空列表
"""
list.clear()
print(list)

 

5.元组

 

Python 的元组与列表类似，不同之处在于元组的元素不能修改。

 

元组使用小括号，列表使用方括号

创建元组

#!/usr/bin/env python
# -*- coding:utf-8 -*-
tup = (‘a‘,‘b‘,‘c‘)
基本操作：
  • 索引
  • 切片
  • 循环
  • 长度
  • 包含
#!/usr/bin/env python
# -*- coding:utf-8 -*-
list = [‘a‘, ‘b‘, ‘c‘]

"""
tuple(seq)
将列表转换为元组
"""
tup = tuple(list)
print(tup)

 

6.字典

字典的每个键值(key=>value)对用冒号(:)分割，每个对之间用逗号(,)分割，整个字典包括在花括号({})中

创建字典

person = {"name": "liu", ‘age‘: 18}

键必须是唯一的，值不必

　　常用操作：

  • 索引
#!/usr/bin/env python
# -*- coding:utf-8 -*-

dic = {
    "name":"mary","age":20
}

dic1 = dic["name"]
print(dic1)

 

  • 新增
#!/usr/bin/env python
# -*- coding:utf-8 -*-

dic = {
    "name":"mary","age":20
}

dic["address"] = "beijing"
print(dic)

 

  • 删除
#!/usr/bin/env python
# -*- coding:utf-8 -*-

dic = {
    "name":"mary","age":20
}

dic["address"] = "beijing"
del dic["age"]
print(dic)

 

  • 键、值、键值对
  • 循环
#!/usr/bin/env python
# -*- coding:utf-8 -*-

dic = {
    "name":"mary","age":20
}

for key,value in dic.items():
    print(key,value)

 

  • 长度
#!/usr/bin/env python
# -*- coding:utf-8 -*-

dic = {
    "name":"mary","age":20
}

print(len(dic))

字典内建函数

技术分享 
class dict(object):
    """
    dict() -> new empty dictionary
    dict(mapping) -> new dictionary initialized from a mapping object‘s
        (key, value) pairs
    dict(iterable) -> new dictionary initialized as if via:
        d = {}
        for k, v in iterable:
            d[k] = v
    dict(**kwargs) -> new dictionary initialized with the name=value pairs
        in the keyword argument list.  For example:  dict(one=1, two=2)
    """

    def clear(self): # real signature unknown; restored from __doc__
        """ 清除内容 """
        """ D.clear() -> None.  Remove all items from D. """
        pass

    def copy(self): # real signature unknown; restored from __doc__
        """ 浅拷贝 """
        """ D.copy() -> a shallow copy of D """
        pass

    @staticmethod # known case
    def fromkeys(S, v=None): # real signature unknown; restored from __doc__
        """
        dict.fromkeys(S[,v]) -> New dict with keys from S and values equal to v.
        v defaults to None.
        """
        pass

    def get(self, k, d=None): # real signature unknown; restored from __doc__
        """ 根据key获取值，d是默认值 """
        """ D.get(k[,d]) -> D[k] if k in D, else d.  d defaults to None. """
        pass

    def has_key(self, k): # real signature unknown; restored from __doc__
        """ 是否有key """
        """ D.has_key(k) -> True if D has a key k, else False """
        return False

    def items(self): # real signature unknown; restored from __doc__
        """ 所有项的列表形式 """
        """ D.items() -> list of D‘s (key, value) pairs, as 2-tuples """
        return []

    def iteritems(self): # real signature unknown; restored from __doc__
        """ 项可迭代 """
        """ D.iteritems() -> an iterator over the (key, value) items of D """
        pass

    def iterkeys(self): # real signature unknown; restored from __doc__
        """ key可迭代 """
        """ D.iterkeys() -> an iterator over the keys of D """
        pass

    def itervalues(self): # real signature unknown; restored from __doc__
        """ value可迭代 """
        """ D.itervalues() -> an iterator over the values of D """
        pass

    def keys(self): # real signature unknown; restored from __doc__
        """ 所有的key列表 """
        """ D.keys() -> list of D‘s keys """
        return []

    def pop(self, k, d=None): # real signature unknown; restored from __doc__
        """ 获取并在字典中移除 """
        """
        D.pop(k[,d]) -> v, remove specified key and return the corresponding value.
        If key is not found, d is returned if given, otherwise KeyError is raised
        """
        pass

    def popitem(self): # real signature unknown; restored from __doc__
        """ 获取并在字典中移除 """
        """
        D.popitem() -> (k, v), remove and return some (key, value) pair as a
        2-tuple; but raise KeyError if D is empty.
        """
        pass

    def setdefault(self, k, d=None): # real signature unknown; restored from __doc__
        """ 如果key不存在，则创建，如果存在，则返回已存在的值且不修改 """
        """ D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D """
        pass

    def update(self, E=None, **F): # known special case of dict.update
        """ 更新
            {‘name‘:‘alex‘, ‘age‘: 18000}
            [(‘name‘,‘sbsbsb‘),]
        """
        """
        D.update([E, ]**F) -> None.  Update D from dict/iterable E and F.
        If E present and has a .keys() method, does:     for k in E: D[k] = E[k]
        If E present and lacks .keys() method, does:     for (k, v) in E: D[k] = v
        In either case, this is followed by: for k in F: D[k] = F[k]
        """
        pass

    def values(self): # real signature unknown; restored from __doc__
        """ 所有的值 """
        """ D.values() -> list of D‘s values """
        return []

    def viewitems(self): # real signature unknown; restored from __doc__
        """ 所有项，只是将内容保存至view对象中 """
        """ D.viewitems() -> a set-like object providing a view on D‘s items """
        pass

    def viewkeys(self): # real signature unknown; restored from __doc__
        """ D.viewkeys() -> a set-like object providing a view on D‘s keys """
        pass

    def viewvalues(self): # real signature unknown; restored from __doc__
        """ D.viewvalues() -> an object providing a view on D‘s values """
        pass

    def __cmp__(self, y): # real signature unknown; restored from __doc__
        """ x.__cmp__(y) <==> cmp(x,y) """
        pass

    def __contains__(self, k): # real signature unknown; restored from __doc__
        """ D.__contains__(k) -> True if D has a key k, else False """
        return False

    def __delitem__(self, y): # real signature unknown; restored from __doc__
        """ x.__delitem__(y) <==> del x[y] """
        pass

    def __eq__(self, y): # real signature unknown; restored from __doc__
        """ x.__eq__(y) <==> x==y """
        pass

    def __getattribute__(self, name): # real signature unknown; restored from __doc__
        """ x.__getattribute__(‘name‘) <==> x.name """
        pass

    def __getitem__(self, y): # real signature unknown; restored from __doc__
        """ x.__getitem__(y) <==> x[y] """
        pass

    def __ge__(self, y): # real signature unknown; restored from __doc__
        """ x.__ge__(y) <==> x>=y """
        pass

    def __gt__(self, y): # real signature unknown; restored from __doc__
        """ x.__gt__(y) <==> x>y """
        pass

    def __init__(self, seq=None, **kwargs): # known special case of dict.__init__
        """
        dict() -> new empty dictionary
        dict(mapping) -> new dictionary initialized from a mapping object‘s
            (key, value) pairs
        dict(iterable) -> new dictionary initialized as if via:
            d = {}
            for k, v in iterable:
                d[k] = v
        dict(**kwargs) -> new dictionary initialized with the name=value pairs
            in the keyword argument list.  For example:  dict(one=1, two=2)
        # (copied from class doc)
        """
        pass

    def __iter__(self): # real signature unknown; restored from __doc__
        """ x.__iter__() <==> iter(x) """
        pass

    def __len__(self): # real signature unknown; restored from __doc__
        """ x.__len__() <==> len(x) """
        pass

    def __le__(self, y): # real signature unknown; restored from __doc__
        """ x.__le__(y) <==> x<=y """
        pass

    def __lt__(self, y): # real signature unknown; restored from __doc__
        """ x.__lt__(y) <==> x<y """
        pass

    @staticmethod # known case of __new__
    def __new__(S, *more): # real signature unknown; restored from __doc__
        """ T.__new__(S, ...) -> a new object with type S, a subtype of T """
        pass

    def __ne__(self, y): # real signature unknown; restored from __doc__
        """ x.__ne__(y) <==> x!=y """
        pass

    def __repr__(self): # real signature unknown; restored from __doc__
        """ x.__repr__() <==> repr(x) """
        pass

    def __setitem__(self, i, y): # real signature unknown; restored from __doc__
        """ x.__setitem__(i, y) <==> x[i]=y """
        pass

    def __sizeof__(self): # real signature unknown; restored from __doc__
        """ D.__sizeof__() -> size of D in memory, in bytes """
        pass

    __hash__ = None

dict
View Code

 注：一般字符串，只要执行一个功能，会生成一个新内容，原内容不变，追加除外

list,tuple,dict,执行一个功能是原内容进行变化

三.for循环

Python for循环可以遍历任何序列的项目，如一个列表或者一个字符串，格式如下

for value in seq:
    do xx

例

#!/usr/bin/env python
# -*- coding:utf-8 -*-

list = [1,2,5,7]
for i in list:
    print(i)

也可以break,continue

#!/usr/bin/env python
# -*- coding:utf-8 -*-

list = [1,2,5,7]
for i in list:
    if i == 5:
        break
    print(i)
#!/usr/bin/env python
# -*- coding:utf-8 -*-

list = [1,2,5,7]
for i in list:
    if i == 5:
        continue
    print(i)

2.enumrate

为可迭代的对象添加序号

 

#!/usr/bin/env python
# -*- coding:utf-8 -*-

li = [11,22,33]
for k,v in enumerate(li, 1):
    print(k,v)

 

3.range和xrange

指定范围，生成指定的数字

#!/usr/bin/env python
# -*- coding:utf-8 -*-

for i in range(10):
    print(i)

 四.练习

列表，字符串，元组,字典之间相互转换

#!/usr/bin/env python
# -*- coding:utf-8 -*-
st = "hello"
li = ["alec", " aric", "Alex", "Tony", "rain"]
tu = ("alec", " aric", "Alex", "Tony", "rain")
dic = {‘k1‘: "alex", ‘k2‘: ‘ aric‘,  "k3": "Alex", "k4": "Tony"}
#列表转无组
tup = tuple(li)
print(tup)
#元组转列表
lis = list(tu)
print(lis)
#字典转列表
tup_list = list(dic.values())
print(tup_list)
#str转list
str_list = list(st)
print(str_list)

 2.列表操作

更换列表元素

li = [‘a‘,‘b‘]
li[1] = ‘c‘
print(li)

将列表转换为字典的key并按照10开始向后递增

li = [‘a‘,‘b‘,‘c‘]
dic = {}
for key,v in enumerate(li,10):
    print(key,v)
    dic[key]=v
print(dic)

 

 

五.模拟题

1、元素分类

有如下值集合 [11,22,33,44,55,66,77,88,99,90...]，将所有大于 66 的值保存至字典的第一个key中，将小于 66 的值保存至第二个key的值中。
即： {‘k1‘: 大于66的所有值, ‘k2‘: 小于66的所有值}

#!/usr/bin/env python
# -*- coding:utf-8 -*-
"""
需求：有如下值集合 [11,22,33,44,55,66,77,88,99,90]
将所有大于 66 的值保存至字典的第一个key中，将小于 66 的值保存至第二个key的值中
"""

list = [11,22,33,44,55,66,77,88,99,90]
dic = {
    "key1": [],
    "key2": []
}
for i in list:
    if i > 66:
        dic[‘key1‘].append(i)
    else:
        dic[‘key2‘].append(i)
print(dic)

 

 

2、查找
查找列表中元素，移除每个元素的空格，并查找以 a或A开头 并且以 c 结尾的所有元素。
    li = ["alec", " aric", "Alex", "Tony", "rain"]
    tu = ("alec", " aric", "Alex", "Tony", "rain") 
    dic = {‘k1‘: "alex", ‘k2‘: ‘ aric‘,  "k3": "Alex", "k4": "Tony"}\
#!/usr/bin/env python
# -*- coding:utf-8 -*-
"""
查找列表中元素，移动空格，并查找以 a或A开头 并且以 c 结尾的所有元素
"""

li = ["alec", " Aric", "Alex", "Tony", "rain"]
tu = ("alec", " aric", "Alex", "Tony", "rain")
dic = {‘k1‘: "alex", ‘k2‘: ‘ aric‘,  "k3": "Alex", "k4": "Tony"}
list1 = list(tu)
list2 = list(dic.values())
newlist = li + list1 + list2
for i in newlist:
    ret = i.strip()
    if (ret.startswith(‘a‘) or ret.startswith(‘A‘)) and ret.endswith(‘c‘):
        print(ret)

 

 
3、输出商品列表，用户输入序号，显示用户选中的商品
    商品 li = ["手机", "电脑", ‘鼠标垫‘, ‘游艇‘]
#!/usr/bin/env python
# -*- coding:utf-8 -*-

"""
输出商品列表，用户输入序号，显示用户选中的商品
商品 li = ["手机", "电脑", ‘鼠标垫‘, ‘游艇‘]
"""
li = ["手机", "电脑", ‘鼠标垫‘, ‘游艇‘]
for key,i in enumerate(li):
    print(key,i)
inp = input("please input your chose:")
chose = int(inp)
print(li[chose])

 

 

 

4、购物车

功能要求：

  • 要求用户输入总资产，例如：2000
  • 显示商品列表，让用户根据序号选择商品，加入购物车
  • 购买，如果商品总额大于总资产，提示账户余额不足，否则，购买成功。
  • 附加：可充值、某商品移除购物车
goods = [
    {"name": "电脑", "price": 1999},
    {"name": "鼠标", "price": 10},
    {"name": "游艇", "price": 20},
    {"name": "美女", "price": 998},
]

 

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#version:1.1

"""
功能要求：
    要求用户输入总资产，例如：2000
    显示商品列表，让用户根据序号选择商品，加入购物车
    购买，如果商品总额大于总资产，提示账户余额不足，否则，购买成功。
    附加：可充值、某商品移除购物车
"""
"""
1.创建空的购物车列表
2.要求用户输入金额资产
3.输入后列出商品列表
4.用户选择商品，加入购物车
5.结算，如果商品价格大于用户总资产提示余额不足，询问是否删除商品
6.结算资金充裕，提示购买成功，显示余额并退出
"""

goods = [
    {"name": "电脑", "price": 1999},
    {"name": "鼠标", "price": 10},
    {"name": "游艇", "price": 20},
    {"name": "美女", "price": 998},
]
cart ={
    "goods_list":[],
    "goods_prices":[]
}
#用户输入账户总额
money = int(input("Please enter your assets:"))
#列出商品信息
print("Products list:")
while True:
    for key,values in enumerate(goods, 1):
        for i in range(len(goods)):
            if key - 1 == i:
                print(key, goods[i]["name"], goods[i]["price"])
    #用户选择商品
    producets = int(input("You can select the product you like:"))
    print("Selecting Goods:",goods[producets-1]["name"],"cost:",goods[producets-1]["price"])
    #计算选购此商品后余额
    cur_assets = money - goods[producets-1]["price"]
    if cur_assets > 0:
        #如果资金充实将商品加入购物车并结算
        cart[‘goods_list‘].append(goods[producets-1]["name"])
        cart[‘goods_prices‘].append(goods[producets-1][‘price‘])
        #print("Your current balance is:", cur_assets, "￥")
        chose = input("continue,please enter ‘c‘;checked out,enter ‘o‘;show information,enter ‘l‘;quit,enter ‘q‘")
       #查看加入购物车商品信息
        if chose == ‘l‘:
            for prod, val in enumerate(cart["goods_list"], 1):
                print(prod, val)
        #退出
        if chose == "q":
            print("Thank you")
            break
        #继续购物
        if chose == "c":
            continue
        #结账
        if chose == "o":
            total = (sum(cart[‘goods_prices‘]))
            if total > money:
                print("Sorry,your account doesn‘t have a large enough balance")
            # 否则就退出程序，并且输出用户本次消费的情况
            else:
                print("Thanks,cost:", total, "￥", "Account balance：", money - total, "￥")
                break
        else:
            print("error,please try agen")

    else:
        print("Sorry,your account doesn‘t have a large enough balance")
        break

 

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#version1.2
goods = [
    {"name": "电脑", "price": 1999},
    {"name": "鼠标", "price": 10},
    {"name": "游艇", "price": 20},
    {"name": "美女", "price": 998},
]
#用户输入总资产
money = input("请输入总资产:")
asset = int(money)
#定义空购物车
cart = {}
for i in goods:
    print(i["name"],i["price"])
while True:
    i2 = input("请选择商品(y/Y)结算;")
    #如果选择结算退出循环
    if i2.lower() == "y":
        break
    #否则继续购物，
    for item in goods:
        if item["name"] == i2:
            name = item["name"]
            #如果购物车已经有此商品，数量+1
            if name in cart.keys():
                cart[name]["num"] = cart[name]["num"] + 1
            #反之，新增字典
            else:
                cart[name] = {‘num‘: 1,‘sigle_price‘: item["price"]}
    print(cart)
#结账
all_prices = 0
for k,v in cart.items():
    n = v[‘sigle_price‘]
    m = v[‘num‘]
    all_sum = n * m
    all_prices = all_prices + all_sum
    if all_prices > asset:
        print("余额不足")
    else:
        print("消费：",all_prices)

 

 

 

5、用户交互，显示省市县三级联动的选择

 

dic = {
    "河北": {
        "石家庄": ["鹿泉", "藁城", "元氏"],
        "邯郸": ["永年", "涉县", "磁县"],
    }
    "河南": {
        ...
    }
    "山西": {
        ...
    }
 
}

 

#!/usr/bin/env python
# -*- coding:utf-8 -*-
#version:1.1



"""
三级联动
"""
dic = {
    "河北":{
        "石家庄":["鹿泉", "藁城", "元氏"],
        "邯郸":["永年", "涉县", "磁县"]
    },
    "河南":{
        "郑州":["中原区", "二七区"],
        "洛阳":["西宫区","洛龙区"]
    },
    "山西":{
        "太原":["南城区","北城区"],
        "大同":["兴和","丰镇"]
    }
}
for i in dic:
    print(i)
flag = False
for trys in range(3):
    provinces_name = input("Please select provinces:")
    if provinces_name in dic:
        provinces = dic[provinces_name]
        city = provinces.keys()
        while True:
            for citys in city:
                print(citys)
            city_name = input("Please enter the city name: ")
            if city_name in city:
                area_name = dic[provinces_name][city_name]
                for i in area_name:
                    print(i)
            else:
                print("Please try agen:")
                continue
            chose = input("Do you want to quit? quit,enter q;Back to top,enter b.")
            if chose == "q":
                print("The application will exits")
                flag = True
                break
            if chose == "b":
                continue
            else:
                print("The information is incorrect,please try agen:")
        if flag:
            break
else:
    print("Three times error, the program will exit")

 六.知识点补充

　1.字符串构造

#!/usr/bin/env python
# -*- coding: utf-8 -*-
#字符串构造
d = {"name":"Peter","age":20}
t = "insert into tb(%s) VALUES (%s)"

key_list = []
value_list = []
for k,v in d.items():
    key_list.append(k)
    value_list.append("%%(%s)s" %(k))

print(key_list,",".join(key_list))
print(value_list,‘,‘.join(value_list))
sql = t % (‘,‘.join(key_list),‘,‘.join(value_list))
print(sql)

 2.列表推导式

    大多数Python开发者知道使用列表推导式。你不熟悉这一点？ 一个列表推导式是一个创造列表的简短方式:

>>> some_list = [1, 2, 3, 4, 5]
>>> another_list = [ x + 1 for x in some_list ]
>>> another_list
[2, 3, 4, 5, 6]

  从Python 3.1开始(也反向地移植到了Python 2.7),我们可以用同样的方式创建集合和字典:

>>> some_list = [1, 2, 3, 4, 5, 2, 5, 1, 4, 8]
>>> even_set = { x for x in some_list if x % 2 == 0 }
>>> even_set
set([8, 2, 4])

>>> # Dict Comprehensions
>>> d = { x: x % 2 == 0 for x in range(1, 11) }
>>> d
{1: False, 2: True, 3: False, 4: True, 5: False, 6: True, 7: False, 8: True, 9: False, 10: True}

第一个例子中，我们用 some_list 建立了一个元素不重复的集合，但只有偶数。第二个字典的例子中展示了一个字典的创建，这个字典的键是1到10（包括10），值是布尔值，指明该键是不是一个偶数。

另一个值得注意的地方是集合的文法，我们可以这么简单的创建一个集合:

>>>my_set = {1, 2, 1, 2, 3, 4}
>>> my_set
set([1, 2, 3, 4])

3. 使用计数器对象计数

很明显，但很容易遗忘。计数是一个寻常不过的编程任务，而且大多数情形下这不是个难事。不过计数可以更简单。

Python的 collections 库包含一个 dict 的子类，专门解决计数任务:

>>> from collections import Counter
>>> c = Counter(‘hello world‘)
>>> c
Counter({‘l‘: 3, ‘o‘: 2, ‘ ‘: 1, ‘e‘: 1, ‘d‘: 1, ‘h‘: 1, ‘r‘: 1, ‘w‘: 1})
>>> c.most_common(2)
[(‘l‘, 3), (‘o‘, 2)]

 

python数据类型详解及列表字典集合推导式详解

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原文地址：http://www.cnblogs.com/jl-bai/p/5451831.html
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