从python中的文本文件返回多行

Question

I had a function which I wanted to read a file and return multiple values from it though I'm having trouble understanding how this would work. For example if my text file look like this:

John 2543
Jack 2453
Henry 3672
Jane 2405 
Terry 9863

And my code like this:

def function(): 

    file = open('file.txt')    

    for lines in file:
        name, number = lines.split(' ')
        return name

def main():
    print(function())

main()

This only returns a name from one line where as I want the entire first column. I understand that if I did a print function instead of return one that would work. However, in this scenario I would like to return the values so that I can use them in conjunction with my other functions. Thank you.

EDIT:

I also had a follow up question as to how I would print the two columns side by side while dedicating a function to each column. So normally, when I print one column after another it would appear as:

John 
Jack 
Henry 
Jane 
Terry 
2543
2453
3672
2405 
9863

when I want them to appear as:

John 2543
Jack 2453
Henry 3672
Jane 2405 
Terry 9863

Answer 1

When you return a value the function ends and control returns immediately to the function that called it. So when you return inside the loop, you never execute the loop more than once before the function exits and hands its return value to the calling function.

You need to build the entire list first, and then return it.

def function():
    with open('file.txt') as file:
        names = []
        for line in file:
            names.append(line.split()[0])

    return names

or

def function():
    with open('file.txt') as file:
        return [line.split()[0] for line in file]

and use it like this:

def main():
    for name in function():
        print(name)

Answer 2

here is a solution with a generator. yield ing every line of your file may come in handy if your file is large. that prevents that the whole file has to be read into memory.

the contents of the file are then handled in a for loop.

also note the with statement to open the file. this takes care of closing it (even if the program crashes) and is the pythonic way to read from a file.

def function():

    with open('file.txt') as file:

       for line in file:
           name, value = line.split()
           value = int(value)
           yield name, value

# here you can do what you need to for all the data in the file
for name, value in function():
    print(name, value)

i took the liberty to cast value to an int . do not know if that is useful to you...

if you need to change row/column, then you have to read all to memory and you could to this:

data = [(names, values) for names, values in function()]
names = [item[0] for item in data]
values = [item[1] for item in data]

you could then pretty-print that with:

separator = '|'
name_lst = ['{:6s}'.format(name) for name in names]
value_lst = ['{:<6d}'.format(value) for value in values]

# join the lists to str
print(separator.join(name_lst))
print(separator.join(value_lst))

# John  |Jack  |Henry |Jane  |Terry 
# 2543  |2453  |3672  |2405  |9863