Exercise 1: Tracking Total Calls vs. Actual Loads — Possible Solution
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THE CHANGE
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    class ImageProxy:
        def __init__(self, filename):
            self.filename = filename
            self._real_image = None
            self.preload_count = 0          # new

        def display(self):
            self.preload_count += 1         # new — counts every call
            if self._real_image is None:
                self._real_image = RealImage(self.filename)
            return self._real_image.display()

preload_count increments on every single call to display(), regardless
of whether the real image already exists. RealImage.load_count (from
this chapter's own RealImage class, unchanged) still only increments
inside RealImage.__init__ - which only ever runs once per proxy, the
first time _real_image is None.

VERIFYING BOTH COUNTS AFTER FOUR CALLS
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Calling proxy.display() four times in a row on the same ImageProxy
gives:

    display() calls (preload_count): 4
    actual RealImage loads (load_count): 1

WHY THE TWO NUMBERS DIVERGE
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preload_count measures how many times the CLIENT asked to see the
image - every one of those requests is genuine and gets a correct
response. load_count measures how many times the EXPENSIVE underlying
work (creating a RealImage) actually happened - the proxy satisfies
requests 2, 3, and 4 using the same already-loaded RealImage from
request 1, so only request 1 shows up in load_count. This is exactly
the point of a virtual proxy: the client-facing call count and the
real expensive-work count are allowed to be completely different
numbers.

WHY THIS WORKS AS AN ANSWER
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The new preload_count is incremented unconditionally at the very top
of display(), before the lazy-loading check runs, so it faithfully
counts every client call rather than only the ones that trigger a
real load - and the two counts are verified together, with the
difference between them explained directly rather than left
unexplained.