python中a.any()以及&&，||
OO~
posted @ 2013年5月26日 20:26
in python
, 16088 阅读
首先说明一下，在python中是没有&&及||这两个运算符的，取而代之的是英文and和or。其他运算符没有变动。
接着重点要说明的是python中的a.any()，我之所以会涉及到这个函数，是因为我在设计某个分段数值函数时由于不细心犯的错误引起的。a.any()，根据官方解释：
Test whether any elements of an array evaluate to True along an axis.
即针对的是一个list，判断list中的某个元素是否为真，此时只要有一个元素为真，list元素全部输出。下面一个例子更直观的做了解释：
#!/usr/bin/python
#coding=utf8
import numpy as np
def f(data):
for val in data:
if val <= 0.6:
r1 = val*1
print "this is <= 0.6 numbers", r1
if val > 4:
r1 = val*1
print "this is > 4 numbers ", r1
def main():
data = np.arange(0.1, 5.1, 0.5)
if np.any(data > 0.3) and np.any(data <= 1):
r1 = data * 1
print r1
f(data)
if __name__=='__main__':
main()
对应的输出是：
[ 0.1 0.6 1.1 1.6 2.1 2.6 3.1 3.6 4.1 4.6] this is <= 0.6 numbers 0.1 this is <= 0.6 numbers 0.6 this is > 4 numbers 4.1 this is > 4 numbers 4.6
在a.any()中，只要满足条件，整个list就是true的。而我在分段函数计算时，恰恰使用到了a.any()来判断list的范围，在后面的计算中，其实是整个list同时运算然后赋值了，也就将分段函数结果简化成了某一段的所有值。正确的计算分段函数有两中策略，要么像上面的函数f()，要么将list分段带入运算。
这个问题我纠结了一个晚上，最后才发现是a.any()的问题。最开始使用的时候，其真正的用法没有具体熟悉，同时我也该反省我自己，对python语言掌握的实在太菜了！
路漫漫其修远兮，吾将上下而求索~
2013年5月26日 20:32
跪求推荐牛人博客，学习python，敦促自己，得到提高
2013年5月27日 00:18
这个不应该属于 numpy 的使用么？
2013年5月27日 18:10
是啊，range貌似不太支持小数吧！PS：这个问题就是我在用matplotlib绘图时，遇到的！
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