python为什么print(print(‘a’))会出： a none python代码运行，为何后面会显示一个none
python\u4e2da=1\uff0c print('a') \u4f1a\u663e\u793aa\uff0c\u6211\u60f3\u663e\u793a1\u4f60\u7684\u60f3\u6cd5\u662f\u4e0d\u662f\u8fd9\u6837\u7684\uff0c\u6839\u636e\u4e00\u4e2a\u5b57\u7b26\u4e32\u91cf\u627e\u5230\u8fd9\u4e2a\u540d\u5b57\u6240\u5bf9\u5e94\u7684\u90a3\u4e2a\u53d8\u91cf\uff1f\uff1f
\u5982\u679c\u662f\u7684\u8bdd\u4f60\u53ef\u4ee5\u7528eval\u5b9e\u73b0\uff0c
eval\u7684\u4f5c\u7528\u662f\u5c06\u5b57\u7b26\u4e32\u683c\u5f0f\u7684\u53c2\u6570\u5f53\u505a\u8868\u8fbe\u5f0f\u5904\u7406\uff0c\u8fd4\u56de\u8868\u8fbe\u5f0f\u7684\u7ed3\u679c
\u6bd4\u5982\u8fd9\u6837
>>> a = 1>>> a1>>> print(eval('a'))1
\u8fd9\u662f\u56e0\u4e3a\uff0c#\u5982\u679c\u76f4\u63a5\u8c03\u7528\uff0cdef\u91cc\u9762\u5c31\u52a0print\uff0c\u5982\u679c\u8c03\u7528\u7684\u65f6\u5019\u7528print\uff0c\u5219\u7528return\u8fd4\u56de\u503c\uff0c\u5982\u4e0b\uff1adef name2number(name):
if name == 'rock':
return 0
elif name == 'paper':
return 1
elif name == 'scissor':
return 2
else:
print('wrong name')
print(name2number("rock"))
\u6269\u5c55\u8d44\u6599\uff1a
\u5728python\u8bed\u8a00\u4e2d\uff0c\u5bf9\u4e8enone\u9700\u8981\u8bb0\u4f4f\u4ee5\u4e0b\u51e0\u70b9\uff1a
1\u3001None\u662f\u4e00\u4e2a\u7279\u6b8a\u7684\u5e38\u91cf\u3002
2\u3001None\u548cFalse\u4e0d\u540c\u3002
3\u3001None\u4e0d\u662f0\u3002
4\u3001None\u4e0d\u662f\u7a7a\u5b57\u7b26\u4e32\u3002
5\u3001None\u548c\u4efb\u4f55\u5176\u4ed6\u7684\u6570\u636e\u7c7b\u578b\u6bd4\u8f83\u6c38\u8fdc\u8fd4\u56deFalse\u3002
6\u3001None\u6709\u81ea\u5df1\u7684\u6570\u636e\u7c7b\u578bNoneType\u3002\u4f60\u53ef\u4ee5\u5c06None\u590d\u5236\u7ed9\u4efb\u4f55\u53d8\u91cf\uff0c\u4f46\u662f\u4f60\u4e0d\u80fd\u521b\u5efa\u5176\u4ed6NoneType\u5bf9\u8c61\u3002
7\u3001python\u4e2d\u7684None\u5c31\u76f8\u8f83\u4e8eJava\u4e2d\u7684Null\u3002python\u4e2d\u5c31\u6ca1\u6709\u6240\u8c13\u7684NULL\u3002
第二个输出None，是因为方法print('a')没有返回值，所以打印出来就是None。
分开来写：
var x = print('a');
print(x);
因为print（）方法没有返回值，所以x的值是空的。
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