如何在Python中减少数字位数？

Question

I have a "CSV" file with four columns:

rep   par  comm    value
USA   GER  60705    100
USA   GER  607034   200
GER   US   607094   300
US    UK   60709    340

I intend to reduce the values for comm column and change them to four digits numbers as follows:

rep   par  comm    value
USA   GER  6070     100
USA   GER  6070     200
GER   US   6070     300
US    UK   6070     340

For doing this, I have written following code:

infile=csv.reader(open("filepath"))
wfile=open("newfilpath", "wb")
writer=csv.writer(wfile, delimiter=",")
writer.writerow(["rep","par","comm","value"])
infile.next()
for row in infile:
    comm=row[2]
    hs4=comm[0:4]
    writer.writerow([row[0],row[1],hs4,row[3]])
wfile.close()

But for numbers like 60705 and 60709 (which are 5 digits), I get 607 not 6070.
Update: I realized that Python add Zero to the numbers with 5 digits and 60705 becomes 060705 as an example. I do not know how to fix this problem. Here is a my output for the real data:

'ALB,DNK,880390,11678\n'
'ALB,FIN,961420,10377\n'
'ALB,FRA,030741,10857\n'
'ALB,FRA,030749,4300\n'
'ALB,FRA,091050,14861\n'
'ALB,FRA,121190,1049561\n'
'ALB,FRA,130219,7291\n'

All the data that starts with zero are 5 digits in fact and Python adds zero automatically to the data.

Answer 1

It may be that you have a space in front of the 6. You can try the .strip() method to get rid of it. I've also modified your code slightly here:

EDIT : now removes leading zeros

import csv

with open("filepath") as ifile, open("newfilpath", "wb") as wfile:
    infile = csv.reader(ifile)
    writer = csv.writer(wfile)
    writer.writerow(next(infile))
    for row in infile:
        row[2] = row[2].strip().lstrip('0')[:4]
        writer.writerow(row)

Answer 2

I suggest trying following method by using pandas.

import pandas as pd
df=pd.read_csv("test.csv")
print df
t=(df['comm']).astype(str)
for i in t:
    print i[:4]

Output:

   rep  par    comm  value
0  USA  GER   60705    100
1  USA  GER  607034    200
2  GER   US  607094    300
3   US   UK   60709    340
6070
6070
6070
6070

Answer 3

Using a slightly modified code to read the CSV file, I get:

import csv

infile=csv.reader(open("filepath"), delimiter=" ", skipinitialspace=True)
wfile=open("newfilpath", "wb")
writer=csv.writer(wfile, delimiter=",")
writer.writerow(["rep","par","comm","value"])
infile.next()
for row in infile:
    print row
    comm=row[2]
    hs4=comm[0:4]
    writer.writerow([row[0],row[1],hs4,row[3]])


wfile.close()}

With the input:

rep   par  comm    value
USA   GER  60705    100
USA   GER  607034   200
GER   US   607094   300
US    UK   60709    340

Using your code, I get an output of:

rep,par,comm,value
USA,GER,6070,100
USA,GER,6070,200
GER,US,6070,300
US,UK,6070,340

The only thing I can think of is changing the delimiter settings or skipinitialspace when you read in your CSV file.