The if statement takes what kind of objects?

In the following code we have if self.frames, but self.frames is a list. What does that mean?

import tkinter as tk
from PIL import Image, ImageTk
from itertools import count

class ImageLabel(tk.Label):
    '''a label that displays images, and plays them if they are gifs'''
    def load(self, im):
        if isinstance(im, str):
            im = Image.open(im)
        self.loc = 0 
        self.frames = []

        try:
            for i in count(1):
                self.frames.append(ImageTk.PhotoImage(im.copy()))
                im.seek(i)       
        except EOFError:    
            pass

        try:
            self.delay = im.info['duration']
        except:
            self.delay = 100

        if len(self.frames) == 1:
            self.config(image=self.frames[0])
        else:
            self.next_frame()

    def unload(self):
        self.config(image=None)
        self.frames = None

    def next_frame(self):
        if self.frames:
            self.loc += 1
            self.loc %= len(self.frames)
            self.config(image=self.frames[self.loc])
            self.after(self.delay, self.next_frame)

root = tk.Tk()
lbl = ImageLabel(root)
lbl.pack()
lbl.load("name_of_image.gif")
root.mainloop()