Python的imp.reload（）函数不起作用？ [英] Python's imp.reload() function is not working?

问题描述

以下是一个简明的例子：

Here's a concise example:

x.py:

class x:
  var = 'from x.py'

y.py：

class x:
  var = 'from y.py'

test.py

import imp
def write_module(filename):
  fp = open('z.py', 'w')
  fp.write(open(filename).read())
  fp.close()

write_module('x.py')
import z
print(z.x.var) # Prints 'from x.py'
write_module('y.py')
imp.reload(z)
print(z.x.var) # Prints 'from x.py'

我不确定为什么两个打印语句都是一样的。如何让python在reload（）之后使用类x的新定义？

I'm not sure why both print statements are the same. How can I make python use the new definition of class x after reload()?

推荐答案

这是因为文件创建日期（ z.py 及其编译对应 z.pyc ）是相同的，因此Python认为该文件未更改且不会重新编译它。

This happens because the file creation dates (of z.py and its compiled counterpart z.pyc) are identical, so Python thinks that the file is unchanged and doesn't recompile it.

实际上，当我尝试并重新尝试你的代码时，它曾经按预期工作 - 可能是因为这两个文件碰巧是在系统时钟的两侧创建的第二次转换。

Actually, when I was trying and re-trying your code, it once worked as expected - probably because the two files happened to be created on either side of the system clock's second-changeover.

import imp
import time
def write_module(filename):
  fp = open('z.py', 'w')
  fp.write(open(filename).read())
  fp.close()

write_module('x.py')
import z
print(z.x.var) # Prints 'from x.py'
time.sleep(1)  # Wait one second
write_module('y.py')
imp.reload(z)
print(z.x.var) # Prints 'from y.py'

显示预期结果。

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