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python3.x 读取csv遇到的bu

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py3study
发布2020-01-03 11:17:17
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发布2020-01-03 11:17:17
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文章被收录于专栏:python3python3

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)

复制代码

import csv

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

if name == 'main': main()

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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:

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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."""

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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: 复制代码

import csv

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

if name == 'main': main()

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

代码如下:

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# 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')

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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: 复制代码

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')

复制代码

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

[python] view plain copy

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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