在 2 个函数中使用 CSV.Reader，只有一个 function 将读取 csv 文件，而另一个将作为文件未被读取的行为

Question

I do not understand why it is that my program will run the first function getcars() just fine and return all the cars but then when I want to run get_cars_older_than_x_years() it will skip the for loop in the function and not execute the code in the function.

I only get this occurring when I try to call both functions. When I only call one of the functions ie I call get_cars_older_than_x_years() it will execute the code as it should.

import csv, datetime


def get_cars():
    for line in csv_reader:
        print(line[0])


def get_cars_older_than_x_years(x):
    print("Following cars are older than", x, "years old.")
    for line in csv_reader:
        age = datetime.date.today().year - int(line[1])
        if age > x:
            print(line)


with open('cars.csv', 'r') as csv_file:  # read file cars.csv
    csv_reader = csv.reader(csv_file)  # will read the file

    get_cars()
    get_cars_older_than_x_years(10)

Answer 1

The problem is that

csv_reader = csv.reader(csv_file)  # will read the file

doesn't actually read the file. The first thing that enumerates csv_reader will read the file. But any future enumerations come back empty because you have reached the end. You can do the read once when the file is first opened and then use that table in your other calls. An easy way to that is with list() .

import csv, datetime

def get_cars():
    for line in car_table:
        print(line[0])

def get_cars_older_than_x_years(x):
    print("Following cars are older than", x, "years old.")
    for line in car_table:
        age = datetime.date.today().year - int(line[1])
        if age > x:
            print(line)

with open('cars.csv', 'r') as csv_file:  # read file cars.csv
    car_table = list(csv.reader(csv_file))  # will read the file
# exit 'with' so that file closes
get_cars()
get_cars_older_than_x_years(10)