使用Python在另一个函数中使用一个函数中的变量

Question

I have a program that downloads video files Here it is in full, don't worry its a short program.

import pafy

def download():
    url = raw_input('Please enter the path to the video\n')
    video = pafy.new(url)
    vid_title = video.title
    best = video.getbest()
    streams = video.streams
    print(vid_title)
    for stream in streams:
        print(stream)
    print'Resolution: ',best.resolution,'\nExtension : ', best.extension
    user_choice = raw_input("Do you want to download this video\ny or n\n")
    if user_choice == 'y':
        print'Your video will downloaded soon'
        filename = best.download(filepath = '/home/mark/new_projects')
        another_download()
    elif user_choice =='n':
        print'You have chosen not to download a video'
        another_download()


def another_download():
    another_choice = raw_input('Would you like to download another video\ny or n\n')
    if another_choice == 'y':
        download()
    else:
        print'Thank for using my program'

download()

I would like to break it down into smaller functions. I have tried to do this:

def url():
    url = raw_input('Please enter the path to the video\n')
    video = pafy.new(url)
    vid_title = video.title
    best = video.getbest()
    streams = video.streams
    print(vid_title)
    for stream in streams:
        print(stream)
    print'Resolution: ',best.resolution,'\nExtension : ', best.extension

def download():
    user_choice = raw_input("Do you want to download this video\ny or n\n")
    if user_choice == 'y':
        print'Your video will downloaded soon'
        filename = best.download(filepath = '/home/mark/new_projects')
        another_download()
    elif user_choice =='n':
        print'You have chosen not to download a video'
        another_download()

But when I try this I get an error telling me that best has not been declared. I don't want to declare best as a global variable. Is there a way of using a variable from one function inside another function?

Answer 1

Split a big function into smaller ones is a good habit but a more urgent problem is that you should use a main loop and make your functions return instead of chaining them like that.

Right now download() -> another_download() -> download() -> another_download() -> download() -> ..., so if the user wants to download n vids you'll have n * 2 - 1 functions hanging around until the last one finish.

Incidentally return solves your problem :

def url():
    ...
    return best 

def download():
    best = url()
    ...

Answer 2

There are a couple options for you here. I will try and lay them out best I can.

Option 1: Assuming you are calling download() first, you can have url() return what you need and store that in a variable in the download() method:

def url():
    url = raw_input('Please enter the path to the video\n')
    video = pafy.new(url)
    vid_title = video.title
    best = video.getbest()
    streams = video.streams
    print(vid_title)
    for stream in streams:
        print(stream)
    print'Resolution: ',best.resolution,'\nExtension : ', best.extension
    return best

def download():
    user_choice = raw_input("Do you want to download this video\ny or n\n")
    if user_choice == 'y':
        best = url()
        print'Your video will downloaded soon'
        filename = best.download(filepath = '/home/mark/new_projects')
        another_download()
    elif user_choice =='n':
        print'You have chosen not to download a video'
        another_download()

Option 2: You could use global variables, though I don't know the ramifications of using them in this case:

best = None
def url():
    global best
    url = raw_input('Please enter the path to the video\n')
    video = pafy.new(url)
    vid_title = video.title
    best = video.getbest()
    streams = video.streams
    print(vid_title)
    for stream in streams:
        print(stream)
    print'Resolution: ',best.resolution,'\nExtension : ', best.extension

def download():
    global best
    user_choice = raw_input("Do you want to download this video\ny or n\n")
    if user_choice == 'y':
        print'Your video will downloaded soon'
        filename = best.download(filepath = '/home/mark/new_projects')
        another_download()
    elif user_choice =='n':
        print'You have chosen not to download a video'
        another_download()

I think either of these solutions will give you what you want, but I would recommend the first in this specific case as it doesn't seem like a complex program.