I\'m pretty new to Python and am completely confused by .join()
which I have read is the preferred method for concatenating strings.
I tried:
To append a string, just concatenate it with the +
sign.
E.g.
>>> a = "Hello, "
>>> b = "world"
>>> str = a + b
>>> print str
Hello, world
join
connects strings together with a separator. The separator is what you
place right before the join
. E.g.
>>> "-".join([a,b])
'Hello, -world'
Join takes a list of strings as a parameter.
join
takes an iterable thing as an argument. Usually it's a list. The problem in your case is that a string is itself iterable, giving out each character in turn. Your code breaks down to this:
"wlfgALGbXOahekxSs".join("595")
which acts the same as this:
"wlfgALGbXOahekxSs".join(["5", "9", "5"])
and so produces your string:
"5wlfgALGbXOahekxSs9wlfgALGbXOahekxSs5"
Strings as iterables is one of the most confusing beginning issues with Python.
"".join may be used to copy the string in a list to a variable
>>> myList = list("Hello World")
>>> myString = "".join(myList)
>>> print(myList)
['H', 'e', 'l', 'l', 'o', ' ', 'W', 'o', 'r', 'l', 'd']
>>> print(myString)
Hello World
Look carefully at your output:
5wlfgALGbXOahekxSs9wlfgALGbXOahekxSs5
^ ^ ^
I've highlighted the "5", "9", "5" of your original string. The Python join() method is a string method, and takes a list of things to join with the string. A simpler example might help explain:
>>> ",".join(["a", "b", "c"])
'a,b,c'
The "," is inserted between each element of the given list. In your case, your "list" is the string representation "595", which is treated as the list ["5", "9", "5"].
It appears that you're looking for +
instead:
print array.array('c', random.sample(string.ascii_letters, 20 - len(strid)))
.tostring() + strid
join() is for concatenating all list elements. For concatenating just two strings "+" would make more sense:
strid = repr(595)
print array.array('c', random.sample(string.ascii_letters, 20 - len(strid)))
.tostring() + strid
There is a good explanation of why it is costly to use +
for concatenating a large number of strings here
Plus operator is perfectly fine solution to concatenate two Python strings. But if you keep adding more than two strings (n > 25) , you might want to think something else.
''.join([a, b, c])
trick is a performance optimization.