在Python 中，== 和is 的用途不同。 1. == 用於比較兩個(gè)對(duì)象的值是否相等，適用於大多數(shù)需要判斷數(shù)據(jù)內(nèi)容一致性的場(chǎng)景；2. is 用於檢查兩個(gè)變量是否指向內(nèi)存中的同一對(duì)象，主要用於身份識(shí)別，如檢查是否為None。例如，兩個(gè)內(nèi)容相同的列表使用== 返回True，但使用is 返回False。因此，應(yīng)根據(jù)需求選擇合適的操作符：用== 判斷值是否相同，用is 判斷是否為同一個(gè)對(duì)象。

In Python, == and is are both used for comparison, but they do very different things. The short version is:

• == checks if two values are equal.
• is checks if two references point to the exact same object in memory.

That means even if two variables look the same (same value), they might not be the same object — and that's where is and == behave differently.

When to use ==

Use == when you want to compare the values of two objects. This is what most people expect when checking equality.

For example:

 a = [1, 2, 3]
b = [1, 2, 3]

print(a == b) # True

Even though a and b are two separate lists, their contents are the same, so == returns True .

This works with strings, numbers, dictionaries, and basically any time you care about the data being the same, not the identity of the object.

When to use is

Use is when you want to check if two variables refer to the exact same object . It's comparing identities, not values.

Going back to the previous example:

 a = [1, 2, 3]
b = [1, 2, 3]

print(a is b) # False

Here, a and b are two different list objects in memory, even though they contain the same values. So is returns False .

A common use case for is is checking against None , because there's only one instance of None in Python:

 value = get_data()
if value is None:
    print("No data returned")

This is the recommended way to test for None , since it's faster and more explicit than using == .

Gotchas and surprises

Python sometimes reuses small integers or short strings to save memory. That can make is seem like it works when it really shouldn't be used.

For example:

 a = 100
b = 100
print(a is b) # Might return True

a = 1000000
b = 1000000
print(a is b) # Probably returns False

This behavior depends on Python's internal optimizations and shouldn't be relied on.

Other cases to watch out for:

• Using is to compare booleans ( True is True is fine, but again, don't rely on it)
• Comparing empty containers ( [] == [] is True , but [] is [] is False )
• Mutable vs immutable types behaving differently under certain conditions

So just remember:

• Use == when comparing values.
• Use is only when checking identity, especially for None .

Summary

To recap:

• == compares values.
• is compares identities (whether two references point to the same object).
• Only use is for identity checks, especially with None .
• Don't assume small values or strings will always share identity.

基本上就這些。

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