List Methods

列表方法

≈ 20 min · python-lists · Open in WolfCode

Think Python's most-quoted Debugging warning: don't write `t = t.sort()`. sort() returns None.

The trap

The classic mistake

t = [3, 1, 2]
t = t.sort()              # ← BUG: sort() returns None
print(t)                  # None
# Then your next operation on t crashes...

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The fix — `sorted()` and `list(reversed())`

Python · runnable

def sorted_copy(t):
    return sorted(t)

def reversed_copy(t):
    return list(reversed(t))            # reversed() returns an iterator

nums = [3, 1, 4, 1, 5, 9, 2, 6]
print("Sorted  :", sorted_copy(nums))
print("Reversed:", reversed_copy(nums))
print("Original:", nums, "(unchanged)")

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The full cheat-sheet

Operation	In-place (mutates)	New list (preserves)
Sort	`t.sort()`	`sorted(t)`
Reverse	`t.reverse()`	`list(reversed(t))`
Append	`t.append(x)`	`t + [x]`
Remove last	`t.pop()`	`t[:-1]`

When in doubt, prefer the right column — they're safer.