python新手常见错误.docx

当初学 Python 时，想要弄懂 Python 的错误信息的含义可能有点复杂。这里列出了常见的的一些让你程序 crash 的运行时错误。1）忘记在?if?,?elif?,?else?,?for?,?while?,?class?,def?声明末尾添加: (导致 “SyntaxError ：invalid syntax”）该错误将发生在类似如下代码中：/question/89964_62779/?12if spam == 42?print(Hello!)2)使用 = 而不是 ==（导致“SyntaxError: invalid syntax”）?= 是赋值操作符而 == 是等于比较操作。该错误发生在如下代码中：/question/89964_62779/?12if spam = 42:?print(Hello!)3）错误的使用缩进量。（导致“IndentationError：unexpected indent”、“IndentationError：unindent does not match any outer indetation level”以及“IndentationError：expected an indented block”）记住缩进增加只用在以：结束的语句之后，而之后必须恢复到之前的缩进格式。该错误发生在如下代码中：/question/89964_62779/?12345678910111213print(Hello!)?print(Howdy!)?或者：?if spam == 42:?print(Hello!)?print(Howdy!)?或者：?if spam == 42:print(Hello!)4）在?for?循环语句中忘记调用?len()?(导致“TypeError: list object cannot be interpreted as an integer”)通常你想要通过索引来迭代一个list或者string的元素，这需要调用?range()?函数。要记得返回len?值而不是返回这个列表。该错误发生在如下代码中：/question/89964_62779/?123spam = [cat, dog, mouse]for i in range(spam):?print(spam[i])5）尝试修改string的值（导致“TypeError: str object does not support item assignment”）string是一种不可变的数据类型，该错误发生在如下代码中：/question/89964_62779/?123spam = I have a pet cat.spam[13] = rprint(spam)而你实际想要这样做：/question/89964_62779/?123spam = I have a pet cat.spam = spam[:13] + r + spam[14:]print(spam)6）尝试连接非字符串值与字符串（导致 “TypeError: Cant convert int object to str implicitly”）该错误发生在如下代码中：/question/89964_62779/?12numEggs = 12print(I have + numEggs + eggs.)而你实际想要这样做：/question/89964_62779/?1234567numEggs = 12print(I have + str(numEggs) + eggs.)?或者：?numEggs = 12print(I have %s eggs. % (numEggs))7）在字符串首尾忘记加引号（导致“SyntaxError: EOL while scanning string literal”）该错误发生在如下代码中：/question/89964_62779/?12345678910print(Hello!)?或者:?print(Hello!)?或者:?myName = Alprint(My name is + myName + . How are you?)8）变量或者函数名拼写错误（导致“NameError: name fooba is not defined”）该错误发生在如下代码中：/question/89964_62779/?12345678910foobar = Alprint(My name is + fooba)?或者:?spam = ruond(4.2)?或者:?spam = Round(4.2)9）方法名拼写错误（导致 “AttributeError: str object has no attribute lowerr”