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python3.x读取csv遇到的bug

1、failedtoset__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

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:
       # ...

 4  

 
 
import numpy as np
import csv
with open ("E:/6Machine Learning/Deep learning/ML2017/hw1.1/hw1/data/train.csv", "r") as csvfile:
    read = csv.DictReader(csvfile)
    price = [row["price"] for row in read]
    a = len(price)
with open("E:/6Machine Learning/Deep learning/ML2017/hw1.1/hw1/data/train.csv", "r") as csvfile:
    read = csv.DictReader(csvfile)
    sqft_living=[row["sqft_living"] for row in read]
    b=len(sqft_living)
read 完这个file以后file就被释放了需要再次读取才能读其他的列???


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