CSV文件写入，需要将特定行写入新的csv文件

Question

I have to write a code that takes a csv file and extracts data related to passenger data from the titanic. I need to take from this file and write a new file that contains the passengers in third class that survived (only this) and the header.

I have provided my code(in text) I have written so far. It works for the test case (it print the #5), but my target_data_file is empty I believe?

I am looking on how to write these specific lines into my target_data_file . I am thinking it should be something along the lines of a for loop with if survived == str(1) and pclass == str(3) , write to Target_data_file .

Not sure though!

Thanks!

import csv
from copy import deepcopy

def third_survived(source_data_file, target_data_file):
    """(str, str) -> int
    Input: Source data is the name of a .csv file containing a subset of the 
    Titanic passenger data, and target_data, the name of a new csv file to be 
    created.
    Output: This function will create a new .csv file named target_data_file and 
    write in it the lines from source_data_file that correspond to the third class 
    passengers who survived the sinking. The function returns the number of lines 
    written to target_data_file.

    >>>third_survived('titanic_some.csv', 'titanic_target.csv')
    5
    """

    with open (str(source_data_file), 'r') as file:
        data_reader=csv.reader(file)
        data_orig=[]
        for row in data_reader:
            data_orig.append(row)

    count= 0
    for elements in range(1,len(data_orig)):
        survived=data_orig[elements][1]
        pclass=data_orig[elements][2]
        if survived == str(1) and pclass == str(3):
            count +=1

    with open(str(target_data_file), 'w') as newfile:
        data_writer=csv.writer(newfile)


        if count == 0:
            return data_orig[0]
        else:
            return count

Answer 1

You could write into the target_data_file along with the counting loop (and you don't need the data_orig list). That is:

def third_survived(source_data_file, target_data_file):
    count= 0
    with open (str(source_data_file), 'r') as file:
        data_reader=csv.reader(file)
        with open(str(target_data_file), 'w') as newfile:
            data_writer=csv.writer(newfile)
            for row in data_reader:
                survived=row [1]
                pclass=row [2]
                if survived == "1" and pclass == "3":
                    count +=1
                    data_writer.writerow(row)

    return count

If you are still keen to return the first row if the count is zero (contradicting your documentation) - you could add

first_row = None

right before the definition of count , and in each iteration check

if first_row is None:
    first_row = row

And in the end return

if count == 0:
    return first_row
return count