why i have the output of [None, None, None]

[length power]

x=['','x1','x2','x3',' ']

x ['', 'x1', 'x2', 'x3', ' ']
[print("ok") for it in x if it.strip() !=""]

ok
ok
ok
[None, None, None]

i understand there are three 'ok' in the output,but why i have the output
of [None, None, None]

 

[Jussi Piitulainen]

x=['','x1','x2','x3',' ']
x ['', 'x1', 'x2', 'x3', ' ']
[print("ok") for it in x if it.strip() !=""]

ok
ok
ok
[None, None, None]

i understand there are three 'ok' in the output,but why i have the
output of [None, None, None]

It's a list containing the values from three invocations of print.
You get it because you asked for it.

|>>> print("ok") == None
|ok
|True
|>>> print("ok") != None
|ok
|False
|>>> [(print("ok") or "die") for x in (1,2,3)]
|ok
|ok
|ok
|['die', 'die', 'die']
|>>> [print("ok") for x in (1,2,3)] and print("What do you want it to be?")
|ok
|ok
|ok
|What do you want it to be?
|>>>

(That last one actually returns None to the interpreter, which
promptly does not print it.)

 

[Rustom Mody]

This is called imperative programming:

for it in x:
.... if it.strip() != '':
.... print ("Ok")

This is called functional programming:

[y for y in x if y.strip() != '']

['x1', 'x2', 'x3']

What you have is a confusion:
print is imperative
comprehension is functional
You should not mix them like that