python中列表的修改函数和替换字符串

Question

There are two skeleton examples after the function code, called "pets" and "movies"

Need help with my code below because errors keep popping up.

The code:

def cleaner(list1):
    for ele in list1:
        if ele == ['a']['the']['and']:
        print('X')



movies = ["I","watched","a","funny","and","good","movie"]
cleaner(movies)
print(movies)

Answer 1

1. Your if ele == ['a']['the']['and']: means nothing, how a variable could be equal to 3 lists with ones items each? (that syntax doesn't even exists

2. You don't replace anything, you're just printing, your need to change the value inside the list

---

Here the fix, that modifies inplace the list

def cleaner(list1):
    for i, ele in enumerate(list1):
        if ele in ['a', 'the', 'and']:
            list1[i] = 'X'

pets = ["the", "dog", "and", "a", "cat"]
cleaner(pets)
print(pets)

Here the version that returns a new list, and so require assignement on output

def cleaner(list1):
    blacklist = ['a', 'the', 'and']
    return ['X' if x in blacklist else x for x in list1]

pets = ["the", "dog", "and", "a", "cat"]
pets = cleaner(pets)
print(pets)

Answer 2

def cleaner(list1):
    for ele in list1:
        if ele == ['a']['the']['and']:
        print('X')

The problem is with your if statement. You have to check each case separately.

if ele=="a" or ele=="the" or ele=="and":

Because what you did there is not a valid Python expression.

Answer 3

If you want to modify the contents of a list of immutable objects (strings are immutable in python), you need to do something different than for ele in list . because changing ele will not actually change the contents of the list. (Although, you are not even doing that, you're just printing "X", but I assume that's what you want to do). You can do this instead, which will modify the list in-place:

def cleaner(list1):
    for i in range(len(list1)):
        if list1[i] in ['a', 'the', 'and']:
            list1[i] = 'X'

pets = ["the","dog","and","a","cat"]
cleaner(pets)

Or, an even more elegant approach:

def cleaner(item):
    if item in ['a', 'the', 'and']:
        return 'X'
    else:
        return item


pets = ["the","dog","and","a","cat"]
cleaned_pets = list(map(cleaner, pets))