I want to understand why and how python treats below example as string when it is actually a list. Does join(expression) treats expression as string?

EXAMPLE 1

```
available_letters = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i',
                     'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r',
                     's', 't', 'u', 'v', 'w', 'x', 'y', 'z']

print 'Available letters: ' + ''.join(available_letters)

```

When I check type of `' '.join(available_letters)` ,it has type string.
But if I use

```
print 'Available letters: ' + available_letters

```

then I get error cannot concatenate a string and a list.