Python `print` 将额外的文本传递给 sys.stdout? [英] Python `print` passing extra text to sys.stdout?

问题描述

这可能是我遗漏的一些愚蠢的东西，但它确实让我挂断了我正在编写的一个更大的项目(c 扩展).

为什么 print "Hello, World!" 将 None 和一个额外的 \n 传递给 sys.stdout> 在这里?

<预><代码>>>>导入系统>>>类 StdOutHook:... def write(self, text):... sys.__stdout__.write("stdout hook 接收到文本:%s\n" % repr(text))...>>>类 StdErrHook:... def write(self, text):... sys.__stderr__.write("stderr hook 接收到文本:%s\n" % repr(text))...>>>sys.stdout = StdOutHook()>>>sys.stderr = StdErrHook()>>>>>>定义 x():...打印你好，世界！"...>>>>>>打印 x()标准输出挂钩收到文本:你好，世界！"标准输出挂钩收到文本:'\n'标准输出挂钩收到文本:无"标准输出挂钩收到文本:'\n'>>>

解决方案

print x() 打印 x() 的返回值，隐式 None

将 print "Hello world" 替换为 return "Hello world" 或将 print x() 替换为 x()

This is probably something stupid I am missing but it has really got me hung up on a larger project (c extension) that I am writing.

Why is print "Hello, World!" passing None and an extra \n to sys.stdout here?

>>> import sys
>>> class StdOutHook:
...     def write(self, text):
...         sys.__stdout__.write("stdout hook received text: %s\n" % repr(text))
... 
>>> class StdErrHook:
...     def write(self, text):
...         sys.__stderr__.write("stderr hook received text: %s\n" % repr(text))
... 
>>> sys.stdout = StdOutHook()
>>> sys.stderr = StdErrHook()
>>> 
>>> def x():
...     print "Hello, World!"
... 
>>> 
>>> print x()
stdout hook received text: 'Hello, World!'
stdout hook received text: '\n'
stdout hook received text: 'None'
stdout hook received text: '\n'
>>> 

解决方案

print x() prints the return value of x() which is implicitly None

Either replace print "Hello world" with return "Hello world" or replace print x() with x()

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