Is Python a

Moreover, the iterator version has been greatly optimized by Python, so it should runfaster as well.As mentioned in the earlier sidebar “Why You Will Care: File Scanners,” it’s alsopossible to read a file line by line with a while loop:>>> f = open('script1.py')>>> while True:... line = f.readline( )... if not line: break... print line.upper( ),......same output...However, this will likely run slower than the iterator-based for loop version becauseiterators run at C language speed inside Python, whereas the while loop version runsPython byte code through the Python virtual machine. Any time we trade Pythoncode for C code, speed tends to increase.Other Built-in Type IteratorsTechnically, there is one more piece to the iteration protocol. When the for loopbegins, it obtains an iterator from the iterable object by passing it to the iter built-infunction; the object returned has the required next method. This becomes obvious ifwe look at how for loops internally process built-in sequence types such as lists:>>> L = [1, 2, 3]>>> I = iter(L) # Obtain an iterator object>>> I.next( ) # Call next to advance to next item1>>> I.next( )2>>> I.next( )3>>> I.next( )Traceback (most recent call last):File "", line 1, in I.next( )StopIterationBesides files and physical sequences like lists, other types have useful iterators aswell. The classic way to step through the keys of a dictionary, for example, is torequest its keys list explicitly:>>> D = {'a':1, 'b':2, 'c':3}>>> for key in D.keys( ):... print key, D[key]...a 1c 3b 2262 | Chapter 13: while and for Loops