python csv reader - convert string to int on the for line when iterating

问题:

I'm interested in not having to write map the int function to the tuple of strings where I currently have it. See the last part of my example:

import os import csv  filepath =  os.path.normpath("c:/temp/test.csv")  individualFile = open(filepath,'rb') dialect = csv.Sniffer().sniff(individualFile.read(1000))  individualFile.seek(0) reader = csv.reader(individualFile,dialect)  names = reader.next()  print names  def buildTree(arityList):     if arityList == []:         return 0                 else:         tree = {}         for i in xrange(arityList[0][0],arityList[0][1]+1):             tree[i] = buildTree(arityList[1:])         return tree   census = buildTree([(1,12),(1,6),(1,4),(1,2),(0,85),(0,14)])  for m, f, s, g, a, c, t in reader:     try:         m,f,s,g,a,c,t = map(int,(m,f,s,g,a,c,t))         census[m][f][s][g][a][c] += t     except:         print "error"         print m, f, s, g, a, c, t         break    

What I want to do is something like this:

for m, f, s, g, a, c, t in map(int,reader):     try:         census[m][f][s][g][a][c] += t     except:         print "error"         print m, f, s, g, a, c, t         break     

I try this and I get the following error:

TypeError: int() argument must be a string or a number, not 'list' 

I'm having trouble understand this error message. I thought reader was an iterable object - not a list. It returns a list for each iteration, but it itself is not a list, correct? I guess that is more of a side question. What I really want to know is if there is a way to do what I am trying to do. Sorry for the code that doesn't really relate, but I thought I would include my whole example. Feel free to tear it to bits! :) I'm wondering if it might be better to just have one dict where the key is a tuple instead of this nested dictionary stuff, but even so, I'm still interested in figuring out my question.

回答1:

what you want is something like:

def int_wrapper(reader):     for v in reader:         yield map(int, v) 

Your code would then look like:

reader = csv.reader(individualFile,dialect) reader = int_wrapper(reader)  # all that other stuff  for m, f, s, g, a, c, t in reader:     try:         census[m][f][s][g][a][c] += t     except:         print "error"         print m, f, s, g, a, c, t         break     

This is just using a generator function to wrap the reader and convert the input to integers.

The origin of the TypeError is that reader is a generator function which yields lists of values. When you apply map to it, you are applying map to a 'list' of lists. This is different than applying map to a list of values which you do when you write it out the long way.

For illustration, another way to do it is

for m, f, s, g, a, c, t in (map(int, v) for v in reader):     # code 

This just uses an in situ generator expression instead of defining a function. It's a matter of taste.

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