Variants of string concatenation?

Question

Out of the following two variants (with or without plus-sign between) of string literal concatenation:

• What's the preferred way?
• What's the difference?
• When should one or the other be used?
• Should non of them ever be used, if so why?
• Is join preferred?

Code:

>>> # variant 1. Plus
>>> 'A'+'B'
'AB'
>>> # variant 2. Just a blank space
>>> 'A' 'B'
'AB'
>>> # They seems to be both equal
>>> 'A'+'B' == 'A' 'B'
True

Answer 1

Juxtaposing works only for string literals:

>>> 'A' 'B'
'AB'

If you work with string objects:

>>> a = 'A'
>>> b = 'B'

you need to use a different method:

>>> a b
    a b
      ^
SyntaxError: invalid syntax

>>> a + b
'AB'

The + is a bit more obvious than just putting literals next to each other.

One use of the first method is to split long texts over several lines, keeping indentation in the source code:

>>> a = 5
>>> if a == 5:
    text = ('This is a long string'
            ' that I can continue on the next line.')
>>> text
'This is a long string that I can continue on the next line.'

''join() is the preferred way to concatenate more strings, for example in a list:

>>> ''.join(['A', 'B', 'C', 'D'])
'ABCD'