Python易忽视知识点小结
这里记录Python中容易被忽视的小问题
一、input(...)和raw_input(...)
#简单的差看帮助文档input(...)和raw_input(...)有如下区别
>>> help(input)
Help on built-in function input in module __builtin__:
input(...)
input([prompt]) -> value
Equivalent to eval(raw_input(prompt)).
>>> help(raw_input)
Help on built-in function raw_input in module __builtin__:
raw_input(...)
raw_input([prompt]) -> string
Read a string from standard input. The trailing newline is stripped.
If the user hits EOF (Unix: Ctl-D, Windows: Ctl-Z+Return), raise EOFError.
On Unix, GNU readline is used if enabled. The prompt string, if given,
is printed without a trailing newline before reading.
#可见 input会根据输入的内容eval结果来返回值，即输入纯数字，则得到的就是纯数字
# raw_input返回的才是字符串
#test：
>>> a = input("输入数字")
输入数字1
>>> type(a)
<type 'int'>
>>> b=raw_input("输入数字")
输入数字1
>>> type(b)
<type 'str'>
ps:在python3.0以后的版本中,raw_input和input合体了,取消raw_input,并用input代替,所以现在的版本input接收的是字符串
二、python三目运算符
虽然Python没有C++的三目运算符(?:)，但也有类似的替代方案，
那就是
1、 true_part if condition else false_part
>>> 1 if True else 0 1 >>> 1 if False else 0 0 >>> "True" if True else "False" 'True' >>> "True" if True else "False" 'Falser'
2、 (condition and [true_part] or [false_part] )[0]
>>> (True and ["True"] or ["False"])[0] 'True' >>> (False and ["True"] or ["False"])[0] 'False' >>>
三、获得指定字符串在整个字符串中出现第N次的索引
# -*- coding: cp936 -*-
def findStr(string, subStr, findCnt):
listStr = a.split(subStr,findCnt)
if len(listStr) <= findCnt:
return -1
return len(string)-len(listStr[-1])-len(subStr)
#test
a = "12345(1)254354(1)3534(1)14"
sub = "(1)"
N = 2 #查找第2次出现的位置
print findStr(a,sub,N)
N = 10 #查找第10次出现的位置
print findStr(a,sub,N)
#结果
#>>>
#14
#-1
四、enumerate用法：
遍历序列的时候，可能同时需要用到序列的索引和对应的值，这时候可以采用enumerate方法进行遍历
enumerate的说明如下：
>>> help(enumerate)
Help on class enumerate in module __builtin__:
class enumerate(object)
| enumerate(iterable[, start]) -> iterator for index, value of iterable
|
| Return an enumerate object. iterable must be another object that supports
| iteration. The enumerate object yields pairs containing a count (from
| start, which defaults to zero) and a value yielded by the iterable argument.
| enumerate is useful for obtaining an indexed list:
| (0, seq[0]), (1, seq[1]), (2, seq[2]), ...
|
| Methods defined here:
|
| __getattribute__(...)
| x.__getattribute__('name') <==> x.name
|
| __iter__(...)
| x.__iter__() <==> iter(x)
|
| next(...)
| x.next() -> the next value, or raise StopIteration
|
| ----------------------------------------------------------------------
| Data and other attributes defined here:
|
| __new__ = <built-in method __new__ of type object>
| T.__new__(S, ...) -> a new object with type S, a subtype of T
五、遍历序列的方法
>>> List = ['a','b','c'] >>> for index, value in enumerate(List): print index, value 0 a 1 b 2 c >>>
六、使用python random模块的sample函数从列表中随机选择一组元素
import List = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] slice = random.sample(List, 5) #从List中随机获取5个元素，作为一个片断返回 print slice print List #原有序列并没有改变。
七、用json打印包含中文的列表字典等
# -*- coding:utf-8 -*-
import json
#你的列表
listA = [{'path': ['[AWS] \xe7\xbe\x8e\xe5\xb0\x91\xe5\xa5\xb3\xe6\x88\x98\xe5\xa3\xab Sailor Moon Crystal - Moon Pride MV[BIG5][BDrip 1080p x264 AAC][6E5CFE86].mp4'], 'length': 131248608L}, {'path': ['[AWS] \xe7\xbe\x8e\xe5\xb0\x91\xe5\xa5\xb3\xe6\x88\x98\xe5\xa3\xab Sailor Moon Crystal - Moon Pride MV[BIG5][BDrip 720p x264 AAC][639D304A].mp4'], 'length': 103166306L}, {'path': ['[AWS] \xe7\xbe\x8e\xe5\xb0\x91\xe5\xa5\xb3\xe6\x88\x98\xe5\xa3\xab Sailor Moon Crystal - Moon Pride MV[BIG5][BDrip 480p x264 AAC][5A81BACA].mp4'], 'length': 75198408L}]
#打印列表
print json.dumps(listA, encoding='UTF-8', ensure_ascii=False)
输出结果：
>>>
[{"path": ["[AWS] 美少女战士 Sailor Moon Crystal - Moon Pride MV[BIG5][BDrip 1080p x264 AAC][6E5CFE86].mp4"], "length": 131248608}, {"path": ["[AWS] 美少女战士 Sailor Moon Crystal - Moon Pride MV[BIG5][BDrip 720p x264 AAC][639D304A].mp4"], "length": 103166306}, {"path": ["[AWS] 美少女战士 Sailor Moon Crystal - Moon Pride MV[BIG5][BDrip 480p x264 AAC][5A81BACA].mp4"], "length": 75198408}]
希望本文所述对大家的Python程序设计有所帮助。
