Let me break this down clearly for you—Python's chained comparisons are one of those neat syntax features that mirror how we write math, and they're super useful for readability and efficiency.

First: How does a <= b < c work in Python? #

In Python, when you write a chained comparison like self.location[0] <= pos[0] < self.location[0] + TILE_WIDTH, it's exactly equivalent to writing:

self.location[0] <= pos[0] and pos[0] < self.location[0] + TILE_WIDTH

The key difference is that in the chained version, the middle value (pos[0] here) is only evaluated once. In the split and version, it gets evaluated twice—this doesn't matter much for simple variables like pos[0], but for complex expressions (like a function call), it saves computation time.

Calculating inside_hor #

Let's map this to your code:

• self.location[0] is the left edge of your tile
• self.location[0] + TILE_WIDTH is the right edge of your tile
• pos[0] is the x-coordinate of the position you're checking

So inside_hor will be True only if the x-coordinate of pos is:

1. Greater than or equal to the tile's left edge (self.location[0] <= pos[0])
2. Less than the tile's right edge (pos[0] < self.location[0] + TILE_WIDTH)

In short: Is the x-position within the horizontal bounds of the tile?

Why use chained comparisons instead of splitting into and? #

Two big reasons:

• Readability: It's exactly how you'd write the condition in math (e.g., "x is between a and b, inclusive of a but exclusive of b"). It's more intuitive at a glance than reading two separate and-joined conditions.
• Efficiency: As mentioned earlier, the middle expression is only computed once. For simple values this is trivial, but for expensive operations (like a database query or complex calculation), it's a nice performance win.

Alternative Implementations #

If you prefer to write it explicitly (maybe for clarity when teaching, or if you're more comfortable with the split syntax), you can absolutely break it into separate conditions:

Option 1: Split into and statements

def is_selected(self, pos):
    # Calculate horizontal bounds
    tile_left = self.location[0]
    tile_right = tile_left + TILE_WIDTH
    # Check horizontal condition
    inside_hor = tile_left <= pos[0] and pos[0] < tile_right
    
    # Calculate vertical bounds
    tile_bottom = self.location[1] - TILE_HEIGHT
    tile_top = self.location[1]
    # Check vertical condition
    inside_vert = tile_bottom <= pos[1] and pos[1] <= tile_top
    
    return inside_hor and inside_vert

Option 2: Use intermediate variables for extra clarity

You could even make each condition super explicit by assigning variables to coordinates:

def is_selected(self, pos):
    x_pos, y_pos = pos[0], pos[1]
    tile_x, tile_y = self.location[0], self.location[1]
    
    x_in_bounds = tile_x <= x_pos < tile_x + TILE_WIDTH
    y_in_bounds = (tile_y - TILE_HEIGHT) <= y_pos <= tile_y
    
    return x_in_bounds and y_in_bounds

This still uses chained comparisons, but the variable names make the intent even easier to parse at a glance.

At the end of the day, the chained comparison syntax is Python's idiomatic way to write these range checks—it's widely used and preferred by most Python developers for its conciseness and readability.

内容的提问来源于stack exchange，提问作者user16786182