Python 打印命令行参数时没有额外输出
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Extra output none while printing an command line argument
提问by CuriousMind
It's my day 1 of learning python. so it's a noob question for many of you. See the following code:
这是我学习 Python 的第一天。所以对你们中的许多人来说这是一个菜鸟问题。请参阅以下代码：
#!/usr/bin/env python
import sys
def hello(name):
name = name + '!!!!'
print 'hello', name
def main():
print hello(sys.argv[1])
if __name__ == '__main__':
main()
when I run it
当我运行它时
$ ./Python-1.py alice
hello alice!!!!
None
Now, I have trouble understanding where this "None"came from?
现在，我很难理解这"None"是从哪里来的？
采纳答案by Thomas Wouters
Count the number of printstatements in your code. You'll see that you're printing "hello alice!!!"in the hellofunction, andprinting the result of the hellofunction. Because the hellofunction doesn't return a value (which you'd do with the returnstatement), it ends up returning the object None. Your printinside the mainfunction ends up printing None.
计算print代码中语句的数量。你会看到，你打印"hello alice!!!"的hello功能，并打印结果hello功能。因为hello函数不返回值（你会用return语句来做），它最终返回 object None。您的print内部main函数最终会打印None。
回答by Sujoy
Change your
改变你的
def main():
print hello(sys.argv[1])
to
到
def main():
hello(sys.argv[1])
You are explicitly printing the return value from your hello method. Since you do not have a return value specified, it returns Nonewhich is what you see in the output.
您正在显式打印 hello 方法的返回值。由于您没有指定返回值，因此它返回None您在输出中看到的内容。
