Using python command if a condition is true in list comprehension?-CodePudding

I wanted to convert the below code into list comprehension.

for i in list:
    if i>b:
        i=5
    else:
        i=0

I tried to use [i if i>b 5 else 0 for i in a] but it resulted in a syntax error. I have also tried [i for i in a if i>b 5 else 0] but that too resulted in a syntax error.

Any solutions?

CodePudding user response：

Your attempt:

[i if i>b 5 else 0 for i in a]

Is close, you just want to give 5 not i like so:

[5 if i>b else 0 for i in a]

Test code:

a = [1,2,3,4,5,6,7,8,9,10]
b = 3
output = [5 if i>b else 0 for i in a]
print(output)

Output:

[0, 0, 0, 5, 5, 5, 5, 5, 5, 5]

This works because the item before the if is given when the statement evaluates to True and the value after the else is given otherwise. So:

output = NumberIfTrue if LogicStatement else NumberIfFalse

is equivalent to :

if LogicStatement:
    output = NumberIfTrue
else:
    output = NumberIfFalse

In your case:

LogicStatement = i>b
NumberIfTrue = 5
NumberIfFalse = 0

Thus you need (as shown above):

5 if i>b else 0

Then you want to apply this to every item in a list which adds:

for i in a

like so:

5 if i>b else 0 for i in a

This is now a generator, since you want a list, you have to surround the generator with [] brackets so that it "generates" the list with the values you want. So just:

[5 if i>b else 0 for i in a]

Then to get the final solution we just assign the result to output so it can be used again:

output = [5 if i>b else 0 for i in a]

CodePudding user response：

In your version

  [i if i>b 5 else 0 for i in list]

The syntax error is right after the i>b. You have the "true value" there, it is in the wrong place. Riffing on your original code

for i in list:
    if i>b: #condition
        i=5 #true action
    else:
        i=0 #false action

The real answer is

[5 if i > b else 0 for i in list]

the pseudo code version

[<true action> if <condition> else <false action> for i in list]