Python中一行声明列表、字典、元组为何会共享引用？

Great question—this is a classic Python gotcha that trips up tons of folks when they’re starting out, so let’s break it down plainly.

First, let’s unpack what’s happening with simple values (like integers) #

When you write a = b = c = 0, here’s the play-by-play:

1. Python creates a single integer object with the value 0.
2. All three variables a, b, and c are set to point to that same 0 object.

But integers are immutable—you can’t alter the value of an existing integer object. When you run a = 10, you’re not changing the original 0; you’re making a point to an entirely new integer object (10). b and c still stick to the original 0, so they stay independent of a’s change.

Now, lists, dictionaries, and (some) tuples work differently #

When you do a = b = c = [], here’s what’s really going on:

1. Python creates one empty list object.
2. All three variables a, b, and c point to that exact same list object.

Lists and dictionaries are mutable—you can modify the object itself without creating a new one. So when you run a.append('Testing'), you’re not making a point to a new list. You’re adding an element directly to the single list that all three variables are referencing. That’s why b and c show the change too—they’re looking at the same underlying object.

For tuples, it’s a bit nuanced: tuples themselves are immutable, but if a tuple contains a mutable object (like a list), the same issue pops up. For example:

a = b = c = ([],)  # A tuple holding an empty list
a[0].append('Testing')
print(b)  # Output: (['Testing'],)

Here, you’re modifying the mutable list inside the tuple, not the tuple itself. If your tuple only has immutable values (like a = b = c = (1, 2)), changing a (e.g., a = (3,4)) would create a new tuple, and b/c wouldn’t change—just like with integers.

How to fix this: Create separate objects #

If you want a, b, and c to be independent lists/dicts, you need to make a unique object for each. Try either of these approaches:

• Separate line assignments:

  a = []
  b = []
  c = []
  

• Unpack multiple objects in one line:

  a, b, c = [], [], []
  

This way, each variable points to its own distinct object, so modifying one won’t affect the others.

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