检查某些东西是否存在的 Pythonic 方法? [英] Pythonic way to check if something exists?

问题描述

这是非常基本的，但我正在编码并开始想知道是否有一种pythonic方法来检查某些东西是否不存在.如果是真的，我会这样做:

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'

但是当我检查某些东西是否不存在时，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'

如果我只关心 kn 有没有办法在没有 else 的情况下检查某些东西是否不存在，那么这似乎是一种浪费?

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，先看后看":

LBYL style, "look before you leap":

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

EAFP 风格，请求原谅比许可更容易":

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

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

在 Python 中编码时更喜欢第二种风格 (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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