在CSV中将CSV数据传输到不同的函数中

Question

i need some help. Basically, i have to create a function to read a csv file then i have to transfer this data into another function to use the data to generate a xml file. Here is my code:

import csv
from xml.etree.ElementTree import Element, SubElement, Comment, tostring
from xml.etree.ElementTree import ElementTree
import xml.etree.ElementTree as etree

def read_csv():
    with open ('1250_12.csv', 'r') as data:
         reader = csv.reader(data)
    return reader

def generate_xml(reader):
    root = Element('Solution')
    root.set('version','1.0')
    tree = ElementTree(root)

    head = SubElement(root, 'DrillHoles')
    head.set('total_holes', '238')

    description = SubElement(head,'description')
    current_group = None
    i = 0
    for row in reader:
        if i > 0:
           x1,y1,z1,x2,y2,z2,cost = row
           if current_group is None or i != current_group.text:
                current_group = SubElement(description, 'hole',{'hole_id':"%s"%i})

                information = SubElement (current_group, 'hole',{'collar':', '.join((x1,y1,z1)),
                                                   'toe':', '.join((x2,y2,z2)),
                                                   'cost':    cost})
        i+=1

def main():
    reader = read_csv()
    generate_xml(reader)

if __name__=='__main__':
   main()

but i get an error when i try to pass reader, the error is: ValueError: I/O operation on closed file

Answer 1

Turning the reader into a list should work:

def read_csv():
      with open ('1250_12.csv', 'r') as data:
           return list(csv.reader(data))

You tried to read from a closed file. list will trigger the reader to read the whole file.

Answer 2

the with statement tells python to clean up the context manager (in this case, a file) once control exits its body. Since functions exit when they return, there's no way to get data out of it with the file still open.

Other answers suggest reading the whole thing into a list, and returning that; this works, but may be awkward if the file is very large.

Fortunately, we can use generators:

def read_csv():
    with open('1250_12.csv', 'r') as data:
        reader = csv.reader(data)
        for row in reader:
            yield row

Since we yield from inside the with , we don't have to clean up the file before getting some rows. Once the data is consumed, (or if the generator is itself cleaned up,) the file will be closed.

Answer 3

So when you read a csv file it is very important to put that file into a list. This is because most operations you cannot perform on the csv.reader file, and that if you do, once you loop through it and it is at the end of the file, you can no longer do anything with it unless you open it and read it again. So lets just change your read_csv function

def read_csv():
    with open ('1250_12.csv', 'r') as data:
         reader = csv.reader(data)
         x = [row for row in reader]
    return x

Now you are manipulating a list and everything should work perfectly!