python列表理解的语法错误

Question

I have a python list of integers with 0 and 1 , now I want to change 0 to -1 , so I'm doing this:

[v[i] = -1 for i in range(len(v)) if v[i] == 0]

then I get syntax error . what's wrong with this?

I also tried the map + lambda but still not working.

map(lambda x: -1 if x == 0 else x, v)

this time it's not syntax error but just didn't change anything to v. what's wrong with this and what's the right solution?

Answer 1

v[i] = -1 is not an expression (assignments are not expressions in Python), it's a statement, therefore it cannot be used in a generator expression like (expr) for item in iterable .

Use a normal for loop:

for i in range(len(v)):
    if v[i] == 0:
        v[i] = -1

Answer 2

你可以用这个

v = [-1 if x == 0 else x for x in v]