What exactly does the .join() method do?


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:

strid = repr(595)
print array.array('c', random.sample(string.ascii_letters, 20 - len(strid)))

and got something like:


Why does it work like this? Shouldn't the 595 just be automatically appended?

11/20/2017 3:20:43 AM

Accepted Answer

Look carefully at your output:

^                 ^                 ^

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"])

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
10/19/2014 2:32:40 AM

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:


which acts the same as this:

"wlfgALGbXOahekxSs".join(["5", "9", "5"])

and so produces your string:


Strings as iterables is one of the most confusing beginning issues with Python.

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