What exactly does the .join() method do?
PythonListStringPython Problem Overview
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)))
.tostring().join(strid)
and got something like:
5wlfgALGbXOahekxSs9wlfgALGbXOahekxSs5
Why does it work like this? Shouldn't the 595 just be automatically appended?
Python Solutions
Solution 1 - Python
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
Solution 2 - Python
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.
Solution 3 - Python
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.
Solution 4 - Python
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
Solution 5 - Python
To expand a bit more on what others are saying, if you wanted to use join to simply concatenate your two strings, you would do this:
strid = repr(595)
print ''.join([array.array('c', random.sample(string.ascii_letters, 20 - len(strid)))
.tostring(), strid])
Solution 6 - Python
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.
Solution 7 - Python
On providing this as input ,
li = ['server=mpilgrim', 'uid=sa', 'database=master', 'pwd=secret']
s = ";".join(li)
print(s)
Python returns this as output :
'server=mpilgrim;uid=sa;database=master;pwd=secret'
Solution 8 - Python
list = ["my", "name", "is", "kourosh"]
" ".join(list)
If this is an input, using the JOIN method, we can add the distance between the words and also convert the list to the string.
This is Python output
'my name is kourosh'
Solution 9 - 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