Question

What does the last line mean in the following code?

import pickle, urllib                                                                                                                                                         handle = urllib.urlopen('http://www.pythonchallenge.com/pc/def/banner.p')   data = pickle.load(handle)   handle.close()    for elt in data:          print ''.join([e[1] * e[0] for e in elt]) 

My attempt to the problem:

• ”.join… uses join -method to empty text
• e[1] * e[0] multiplies two subsequent values in the sequence, e
• I am not sure what is e
• I am not sure, what it means, when you have something before for -loop, like: e[1] * e[0] for e in elt

Answer 1

Maybe best explained with an example:

print ''.join([e[1] * e[0] for e in elt]) 

is the short form of

x = [] for e in elt:   x.append(e[1] * e[0]) print ''.join(x) 

List comprehensions are simply syntactic sugar for for loops, which make an expression out of a sequence of statements.

elt can be an arbitrary object, since you load it from pickles, and e likewise. The usage suggests that is it a sequence type, but it could just be anything that implements the sequence protocol.