用pythonic方式检查是否存在某些东西？ [英] pythonic way to check if something exists?

问题描述

这是非常基本但我编码并开始想知道是否有一种pythonic方法来检查是否存在某些东西。如果它是真的，我就是这样做的：

This is pretty basic but I was coding and started wondering if there was a pythonic way to check if something does not exist. Here's how I do it if its true:

var = 1
if var:
    print 'it exists'

但是当我检查是否存在某些东西时，我经常这样做：

but when I check if something does not exist, I often do something like this:

var = 2
if var:
    print 'it exists'
else:
    print 'nope it does not'

如果所有我关心的都是knis那么看起来就像浪费在没有else的情况下检查是否存在某些东西的方法？

Seems like a waste if all I care about is knIs there a way to check if something does not exist without the else?

推荐答案

LBYL风格，在你跳跃之前看：

LBYL style, "look before you leap":

var_exists = 'var' in locals() or 'var' in globals()

EAFP风格，比允许更容易请求宽恕：

EAFP style, "easier to ask forgiveness than permission":

try:
    var
except NameError:
    var_exists = False
else:
    var_exists = True

在Python编码时首选第二种样式（EAFP），因为它通常更可靠。

Prefer the second style (EAFP) when coding in Python, because it is generally more reliable.

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