why output of 'for in one line' is printed in above lines?-CodePudding

my code is....

names = ['ali', 'parham', 'hasan', 'farhad']
print('names: ', [print(i) for i in names])

and my output is this...

ali
parham
hasan
farhad
names:  [None, None, None, None]

but i want this....

names: ali, parham, hasan, farhad

why what are in the list is 'None'?!

and why the name are in the above lines?!

CodePudding user response：

When you do print('names: ', [print(i) for i in names]) the following happens: To do the first print Python has to evaluate the arguments of the function. The second argument is [print(i) for i in names]. Here you loop over the names, print them and put the result of the call to print in the list. This result is always None.

So after this first step all the names are printed and then you're virtually left with print('names: ', [None, None, None, None]). Now print will output exactly that.

If you want to combine the entries of a list to a string use the strings join method. Here are some examples from the interactive interpreter.

>>> '-'.join(['A', 'B', 'C'])
'A-B-C'
>>> 'x'.join(['A', 'B', 'C'])
'AxBxC'
>>> ' '.join(['A', 'B', 'C'])
'A B C'
>>> values = ['x', 'yy', 'zzz']
>>> '   '.join(values)
'x   yy   zzz'
>>> names = ['ali', 'parham', 'hasan', 'farhad']
>>> ', '.join(names)
'ali, parham, hasan, farhad'

So what you need here is:

print('names:', ', '.join(names))

or with an f-string

print(f"names: {', '.join(names)}")

This will give you names: ali, parham, hasan, farhad.