Python学习过程遇到的Bug不断更新

1、failed to set __main__.__loader__

    兴奋地配置好了Python环境，运行hello.py实例就出现这个异常，着实让人扫兴，百度上搜了下没有找到答案。再去Google了下，发现可能是hello.py文件中包含非英文字符，果然将hello.py放到纯英文路径下就没问题了。

    对于eclipse下使用PyDev的情况，可以用File->Switch Workspace的方法来切换到一个英文路径工作空间目录

2、_csv.Error: iterator should return strings, not bytes (did you open the file in text mode?)

     在用下面的代码处理csv文件时出现这个错误（Python 3)

import csv

def main():
    reader=csv.reader(open('userid.csv', 'rb'))
    for item in reader:
        print(item)

if __name__ == '__main__':
    main()

    经过万能的Google搜索，找到了问题所在：http://bugs.python.org/msg82661 ，下面是部分摘录：

Sorry, folks, we've got an understanding problem here. CSV files are
typically NOT created by text editors. They are created e.g. by "save as
csv" from a spreadsheet program, or as an output option by some database
query program. They can have just about any character in a field,
including \r and \n. Fields containing those characters should be quoted
(just like a comma) by the csv file producer. A csv reader should be
capable of reproducing the original field division. Here for example is
a dump of a little file I just created using Excel 2003:
...

This sentence in the documentation is NOT an error: """If csvfile is a
file object, it must be opened with the ‘b’ flag on platforms where that
makes a difference."""

   虽然这个解释没有告诉我们怎么解决这个问题，但是我根据上面这段话，将代码改成下面这样就OK了：

import csv

def main():
    reader=csv.reader(open('userid.csv', 'r'))
    for item in reader:
        print(item)

if __name__ == '__main__':
    main()

3、UnboundLocalError: local variable 'f' referenced before assignment（f.close()）

    代码如下：

    # Errors and Exceptions
    # 详细文档参考：http://docs.python.org/2/tutorial/errors.html
    try:
        f = codecs.open("noexistfile.txt", "rU", "utf-8")
        text = f.read()
    except Exception:
        sys.stderr.write('读取文件发生IO异常！\n')
    finally:
        f.close()
        sys.stderr.write('finnaly执行！\n')

   这个错误在打开的文件不存在时才会发生。原因是如果文件不存在则f是None，这时在except语句分支中执行f.close()会报一样的错。这与Java里的文件读取异常处理不太一样，正确的做法如下：

  # Errors and Exceptions
    # 详细文档参考：http://docs.python.org/2/tutorial/errors.html
    try:
        f = codecs.open("noexistfile.txt", "rU", "utf-8")
        text = f.read()
        f.close()
    except Exception:
        sys.stderr.write('读取文件发生IO异常！\n')
    finally:
        sys.stderr.write('finnaly执行！\n')

    其他可能的一种情况：http://blog.csdn.net/magictong/article/details/4464024

    文件读写的推荐写法如下（这样不需要显式关闭文件）：

with open("test.txt", "r") as file_handle:
    for line in file_handle:
       # ...

...