带零的csv书写板

Question

I have a working python script that takes a .csv input, takes out the 4 columns that I want, trims all white space, and writes it to a new file. There's only one thing I can't figure out how to do...

import csv,time,string,os,requests
dw = "\\\\network\\folder\\btc.csv"

inv_fields = ["id", "rsl", "number", "color_b4"]

with open(dw) as infile, open("c:\\upload\\log.csv", "wb") as outfile:
    r = csv.DictReader(infile)
    w = csv.DictWriter(outfile, inv_fields, extrasaction="ignore")
    r = (dict((k, v.strip()) for k, v in row.items() if v) for row in r)

    wtr = csv.writer( outfile )
    wtr.writerow(["id", "resale", "number", "favorite_color"])
    for i, row in enumerate(r, start=1):
        row['id'] = i
        w.writerow(row)

print "file successfully saved"

I need to modify the 3rd column, number , either when the input file is being read, or when the output file is being written, so that each value is 9 digits long, padded with zeroes to the left. The input will never be greater than 9, so:

Output:

Input      |    Output
1234       |    000001234
393939392  |    393939392
5          |    000000005

I'm not sure at all how I would go about this though. Any input would be appreciated!

Answer 1

You can conver integers to string first, and then use zfill function.

>> print str(123).zfill(9)
000000123
>> print str(123).zfill(2)
123
>> print str(123).zfill(3)
123
>> print str(123).zfill(4)
0123

Even if you have negative number, you can still use zfill() to fill it.

>>> print(str(-123).zfill(9))
-00000123

Answer 2

As already proposed in the comments, the following works on my machine:

# ...
row['number'] = "{:09d}".format(int(row['number']))
w.writerow(row)

Answer 3

The simplest way would be to just use the zfill() string method on the one field (no need to convert it into a integer first). You can also handle writing the header row in the output file by just calling the csv.DictWriter.writeheader() method:

import csv,time,string,os,requests
dw = "\\\\network\\folder\\btc.csv"

inv_fields = ["id", "rsl", "number", "color_b4"]

with open(dw, 'rb') as infile, open("c:\\upload\\log.csv", "wb") as outfile:
    r = csv.DictReader(infile)
    w = csv.DictWriter(outfile, inv_fields, extrasaction="ignore")

    r = (dict((k, v.strip()) for k, v in row.items() if v) for row in r)

    w.writeheader()
    for i, row in enumerate(r, start=1):
        row['id'] = i
        row['number'] = row['number'].zfill(9)  # added
        w.writerow(row)

print "file successfully saved"