Python學習過程遇到的Bug-不斷更新

1、failed to set __main__.__loader__

    興奮地配置好了Python環境，運行hello.py執行個體就出現這個異常，著實讓人掃興，百度上搜了下沒有找到答案。再去Google了下，發現可能是hello.py檔案中包含非英文字元，果然將hello.py放到純英文路徑下就沒問題了。

    對於eclipse下使用PyDev的情況，可以用File->Switch Workspace的方法來切換到一個英文路徑工作空間目錄

 

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

     在用下面的代碼處理csv檔案時出現這個錯誤（Python 3)

import csvdef main():    reader=csv.reader(open('userid.csv', 'rb'))    for item in reader:        print(item)if __name__ == '__main__':    main()

    經過萬能的Google搜尋，找到了問題所在：http://bugs.python.org/msg82661 ，下面是部分摘錄：

Sorry, folks, we've got an understanding problem here. CSV files aretypically NOT created by text editors. They are created e.g. by "save ascsv" from a spreadsheet program, or as an output option by some databasequery 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 becapable of reproducing the original field division. Here for example isa dump of a little file I just created using Excel 2003:
...

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

   雖然這個解釋沒有告訴我們怎麼解決這個問題，但是我根據上面這段話，將代碼改成下面這樣就OK了：

import csvdef 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()）

    代碼如下：

    # Errors and Exceptions    # 詳細文檔參考：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('讀取檔案發生IO異常！\n')    finally:        f.close()        sys.stderr.write('finnaly執行！\n')

   這個錯誤在開啟的檔案不存在時才會發生。原因是如果檔案不存在則f是None，這時在except語句分支中執行f.close()會報一樣的錯。這與Java裡的檔案讀取異常處理不太一樣，正確的做法如下：

  # Errors and Exceptions    # 詳細文檔參考：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('讀取檔案發生IO異常！\n')    finally:        sys.stderr.write('finnaly執行！\n')

    其他可能的一種情況：http://blog.csdn.net/magictong/article/details/4464024

    檔案讀寫的推薦寫法如下（這樣不需要顯式關閉檔案）：

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

 

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