从 tkinter 标签获取 PhotoImage 对象

Question

有没有办法从tkinter.Label 实例中获取tkinter.PhotoImage 对象？我知道有this question，它有一个部分令人满意的答案，但我真的需要一个PhotoImage 对象：

>>> import tkinter as tk
>>>
>>> root = tk.Tk()
>>>
>>> image1 = tk.PhotoImage(file="img.gif")
>>> image2 = tk.PhotoImage(file="img.gif")
>>>
>>> label = tk.Label(root, image=image1)
>>> label._image_ref = image1
>>> label.cget("image") == image2
False

是否有一个函数可以让我从pyimage 字符串中获取图像对象？ IE。一个从label.cget("image")获得？

---

答案是，apparantly，你不能。最接近的方法是获取图像源（文件或数据）并检查（可能通过散列）两个图像是否相同。 tkinter.PhotoImage没有实现__eq__，所以你不能只比较两个图像以获得相同的数据。这是解决问题的最后一个示例（大部分）：

import hashlib
import os
import tkinter as tk

_BUFFER_SIZE = 65536


def _read_buffered(filename):
    """Read bytes from a file, in chunks.
    Arguments:
    - filename: str: The name of the file to read from.
    Returns:
    - bytes: The file's contents.
    """
    contents = []
    with open(filename, "rb") as fd:
        while True:
            chunk = fd.read(_BUFFER_SIZE)
            if not chunk:
                break
            contents.append(chunk)
        return bytes().join(contents)


def displays_image(image_file, widget):
    """Check whether or not 'widget' displays 'image_file'.
    Reading an entire image from a file is computationally expensive!
    Note that this function will always return False if 'widget' is not mapped.
    This doesn't work for images that were initialized from bytes.
    Arguments:
    - image_file: str: The path to an image file.
    - widget: tk.Widget: A tkinter widget capable of displaying images.
    Returns:
    - bool: True if the image is being displayed, else False.
    """
    expected_hash = hashlib.sha256(_read_buffered(image_file)).hexdigest()
    if widget.winfo_ismapped():
        widget_file = widget.winfo_toplevel().call(
            widget.cget("image"), "cget", "-file"
        )
        if os.path.getsize(widget_file) != os.path.getsize(image_file):
            # Size differs, the contents can never be the same.
            return False
        image_hash = hashlib.sha256(
            _read_buffered(widget_file)
        ).hexdigest()
        return image_hash == expected_hash

Answer 1

tkinter 是 tk 的包装器，PhotoImage 也是 image 的包装器。很明显，您不能只是向后移动并从 image 创建一个 PhotoImage。

但是，由于您可以执行 tk 命令，并且 PhotoImage 和 image 具有相似的结构，因此您最好的选择是这样的：

import tkinter as tk

root = tk.Tk()

image1 = tk.PhotoImage(file="img.gif")
image2 = tk.PhotoImage(file="img.gif")

label = tk.Label(root, image=image1)
label._image_ref = image1

foo = root.call(label.cget('image'), 'cget', '-file')
bar = image2['file']
print('1st image:\t%s\n2nd image:\t%s\nEqual:\t%r' % (foo, bar, foo == bar))

• tk image
• tk photo