Question

I currently encountered a problem:
I want to handle adding strings to other strings very efficiently, so I looked up many methods and techniques, and I figured the “fastest” method.
But I quite can not understand how it actually works:

def method6():
    return ''.join([`num` for num in xrange(loop_count)])

From source (Method 6)

Especially the ([`num` for num in xrange(loop_count)]) confused me totally.

Answer 1

xrange() is a faster (written in C) version of range().

Backtick notation — num, coerces a variable to a string, and is the same as str(num).

[x for x in y] is called a list comprehension, and is basically an one-liner for loop that returns a list as its result. So all together, your code’s semantically equivalent to the following, but faster, because list comprehensions and xrange are faster than for loops and range:

z = []
for i in range(loop_count):
   z.append(str(i))
return "".join(z)