Python - csv.DictWriter（）或writerow（）舍入我的浮动？ [英] Python - csv.DictWriter() or writerow() rounding my floats?

问题描述

我是Python的新手，所以如果这个问题很容易回答，如果我的Python语言有点离题，请原谅我。

我有一个字典我想写一个csv文件，但字典中的浮动在我写它们到文件四舍五入。

舍入发生在哪里，如何防止？

提前感谢！

ps我按照这里的DictWriter示例： http://www.doughellmann.com/PyMOTW/csv/我在Mac上运行Python 2.6.1（10.6 - Snow Leopard）。

---

 ＃my import statement 
 import sys 
 import csv 
  

是我的字典（d）包含：

 >> d = runtime .__ dict__ 
>>>> d 
 {'time_final'：1323494016.8556759，
'time_init'：1323493818.0042379，
'time_lapsed'：198.85143804550171} 
  

这些值确实是浮点数：

 >> type（runtime.time_init）
< type'float'> 
  

然后我设置我的writer并写头和值：

  f = open（log_filename，'w'）
 fieldnames =（'time_init'，'time_final'，'time_lapsed'）
 myWriter = csv.DictWriter（f，fieldnames = fieldnames）
 header = dict（（n，n）for n in fieldnames）
 myWriter.writerow（headers）
 myWriter.writerow（d）
 f.close（）
  

但是当我查看输出文件时，即浮动）：

  time_init，time_final，time_lapsed 
 1323493818.0,1323494016.86,198.851438046 
  

< EOF>

解决方案

看起来像csv 正在使用 float .__ str __ 而不是 float .__ repr __ ：

 >> print repr（1323494016.855676）
 1323494016.855676 
>>>> print str（1323494016.855676）
 1323494016.86 
  

查看 csv source ，这似乎是硬连线的行为。一个解决方法是在csv获取它之前将所有的float值转换到它们的repr。使用类似： d = dict（（k，repr（v））for k，v in d.items（））。

下面是一个实例：

  import sys，csv 
 
d = {'time_final'：1323494016.8556759，
'time_init'：1323493818.0042379，
'time_lapsed'：198.85143804550171 
} 
 
d = dict（（k，repr对于k，v在d.items（））
 
 fieldnames =（'time_init'，'time_final'，'time_lapsed'）
 myWriter = csv.DictWriter（sys.stdout，fieldnames =字段名）
 header = dict（（n，n）for n in fieldnames）
 myWriter.writerow（headers）
 myWriter.writerow（d）
  
 
 
 
此代码生成以下输出：
  time_init，time_final，time_lapsed 
 1323493818.0042379,1323494016.8556759,198.85143804550171 
  
更完善的方法仅对浮点数进行替换：
  d = dict（（k，（repr（v）if isinstance（v，float） 
  
注意，I '只是固定这个问题为Py2.7.3，所以它不应该是一个问题在未来。请参见 http://hg.python.org/cpython/rev/bf7329190ca6  
 
I'm new to Python so please forgive me if this question is easy to answer and if my Python lingo is a bit off.

I have a dictionary that I want to write to a csv file, but the floats in the dictionary are rounded off when I write them to the file.  I want to keep these intact/as is.

Where does the rounding occur and how can I prevent it?

Thanks in advance!

p.s. I followed the DictWriter example here: http://www.doughellmann.com/PyMOTW/csv/ and I'm running Python 2.6.1 on Mac (10.6 - Snow Leopard).



# my import statements
import sys
import csv
Here is what my dictionary (d) contains:
>>> d = runtime.__dict__
>>> d
{'time_final': 1323494016.8556759,
'time_init': 1323493818.0042379,
'time_lapsed': 198.85143804550171}
The values are indeed floats:
>>> type(runtime.time_init)
<type 'float'>
Then I setup my writer and write the header and values:
f = open(log_filename,'w')
fieldnames = ('time_init', 'time_final', 'time_lapsed')
myWriter = csv.DictWriter(f, fieldnames=fieldnames)
headers = dict( (n,n) for n in fieldnames )
myWriter.writerow(headers)
myWriter.writerow(d)
f.close()
But when I look in the output file, I get rounded numbers (i.e., floats):
time_init,time_final,time_lapsed
1323493818.0,1323494016.86,198.851438046
< EOF >
解决方案
It looks like csv is using float.__str__ rather than float.__repr__:
>>> print repr(1323494016.855676)
1323494016.855676
>>> print str(1323494016.855676)
1323494016.86
Looking at the csv source, this appears to be a hardwired behavior.  A workaround is to cast all of the float values to their repr before csv gets to it.  Use something like: d = dict((k, repr(v)) for k, v in d.items()).

Here's a worked-out example:
import sys, csv

d = {'time_final': 1323494016.8556759,
     'time_init': 1323493818.0042379,
     'time_lapsed': 198.85143804550171
}

d = dict((k, repr(v)) for k, v in d.items())

fieldnames = ('time_init', 'time_final', 'time_lapsed')
myWriter = csv.DictWriter(sys.stdout, fieldnames=fieldnames)
headers = dict( (n,n) for n in fieldnames )
myWriter.writerow(headers)
myWriter.writerow(d)
This code produces the following output:
time_init,time_final,time_lapsed
1323493818.0042379,1323494016.8556759,198.85143804550171
A more refined approach will take care to only make replacements for floats:
d = dict((k, (repr(v) if isinstance(v, float) else str(v))) for k, v in d.items())
Note, I've just fixed this issue for Py2.7.3, so it shouldn't be a problem in the future.  See  http://hg.python.org/cpython/rev/bf7329190ca6 

                        
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