how to write csv file using python

Question

i have a python script that read from csv file and store the values in a list, where the values are Dates row[0], float row[10] , Boolean row[11].

the script work perfectly in reading part but when i try to write the selected values to a second CSV file the system create a file with just the headers, and the system crash with displaying this error:

line 62, in
fwriter.writerow("{}:{}:{}".format(row[0],row[10],row[11]))

builtins.IndexError: string index out of range

where is the error in the code?

code:

          import csv

            mydelimeter = csv.excel()
            mydelimeter.delimiter=";"
            myfile = open("C:/Users/test/Documents/R_projects/homework/rdu-weather-history.csv")

            # read the first line in the opened file ==> Header
            myfile.readline()

            myreader=csv.reader(myfile,mydelimeter)

            result=[]

            '''
            create a variable that handle values of the 3 fields
 ==> Date - fastest5secwindspeed - fog
             and display the result where  
                 fog ==> Yes    and highest speed  more than 10.
            '''

            for index ,row in enumerate(myreader):
                try:
                    '''
                    check if the values in the fog colums is == Yes 
                    if ok 
                    check if the column of the "fastwindspeed" 
is  empty ==>  raise Exception
                    check if the value in column of the "fastwindspeed"
 is < 10.0 ==>  raise Exception

                    else  print the results
                    '''
                    if row[11] =="Yes":
                        if row[10] in (None, ""):
                            raise Exception( "this Record has empty value" )
                        if float(row[10]) < 10.0:
                            raise Exception( 'the wind speed  is below 10 mph in ' + row[0] )            
                        print(row[0],row[10],row[11])
                        '''
                        append the result into a list
 in order to use it in the writing of the new csv file  
                        '''
                        result.append(row[0])
                        result.append(row[10])
                        result.append(row[11])
                except Exception as e:
                    print("{}:{}".format(index ,e))
          myfile.close()
             '''
    create a second csv file and append the selected result from the  1st csv file 
    '''  
            with open("C:/Users/test/Documents/Python_Projects/rduSpeedFog.csv", "w") as f:
                headers = ["Date","WindSpeed","Fog"]

                fwriter=csv.writer(f,mydelimeter)

                fwriter.writerow(headers)

                for row in result:


                    fwriter.writerow("{}:{}:{}".format(row[0],row[10],row[11]))

                print("Writing Complete")
            f.close()

after using the answer of @Bamar

i got this result

csv file as result

`result` is a list of strings, not a list of rows. The loop `for row in result:` makes no sense. — Barmar, Feb 24 '18 at 07:25
Why don't you just do that inside the `for index, row in enumerate(myreader):` loop? — Barmar, Feb 24 '18 at 07:26
Why not make use of pandas `to_csv` ? https://stackoverflow.com/a/16923367/6242649 — Udayraj Deshmukh, Feb 24 '18 at 07:48

Barmar · Accepted Answer · 2018-02-24T07:42:07.193

1

In the first loop, each string is put into a separate element of the result list, so it's not a list of rows.

You should change that loop to use:

result.append([row[0], row[10], row[11]])

to append those fields as a list for each row.

In the second loop you're using a csv.writer, so it will add the delimiters, and you shouldn't use format. Just write:

fwriter.writerow(row)

And if you want the field delimiter to be : in the output file, use:

fwriter=csv.writer(f,":")

edited Feb 24 '18 at 07:42

answered Feb 24 '18 at 07:31

Barmar

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@Bamar **first** i tried your answer it write the values but not in good format i will edit my question and add image for the result of csv file **second** what is the meaning of * – Pyt Leb Feb 24 '18 at 07:37
See https://codeyarns.com/2012/04/26/unpack-operator-in-python/ for what `*` means in a function argument. – Barmar Feb 24 '18 at 07:41
You need to use a different delimiter than `mydelimiter` for the output file. – Barmar Feb 24 '18 at 07:42
@Bamar no it seems it worked once i delete the **.format** but i did not understand why with format did not worked as it should although i specified the **right delemiter** – Pyt Leb Feb 24 '18 at 07:48
The argument to `writerow` should be a list of the fields. When you formatted it, there's no list. – Barmar Feb 24 '18 at 07:49
can i write the exception also into the new csv file ?? – Pyt Leb Feb 24 '18 at 07:54
The first loop will have to append those to the `result` array, and then the second loop will need an `if` statement so it can process those rows differently. – Barmar Feb 24 '18 at 07:55
when you said append those to result ? you add the **raised exceptions** to the result list ? – Pyt Leb Feb 24 '18 at 08:02
I meant appending the strings, like `result.append("{}:{}".format(index ,e))` – Barmar Feb 24 '18 at 14:18

score 0 · Answer 2 · answered Feb 24 '18 at 07:32

0

writerow takes a sequence as a parameter, but you are passing a string. Try to pass your values as a list.

answered Feb 24 '18 at 07:32

Ander2

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how to write csv file using python

code:

2 Answers2