练习程序里如何加注释。在你想要临时移除一段代码时，你可以用注解的方式将这段代码临时禁用。
基本练习：
在文本编辑器中，编辑以下内容并保存到ex2.py文件中，同时在终端中运行该文件：
# A comment, this is so you can read your program later.
# Anything after the # is ignored by python.
print "I could have code like this." # and the comment after is ignored
# You can also use a comment to "disable" or comment out a piece of code:
# print "This won't run."
print "This will run."
执行结果：
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