Python Data Persistence – for Keyword
Like many other languages, Python also provides for keywords to construct a loop. However, Python’s for loop is a little different from others. Instead of a count-based looping mechanism, Python’s for loop iterates over each item in a collection object such as list, tuple, and so on.
Python’s sequence-type objects are the collections of items. These objects have an in-built iterator. An iterator is a stream that serves one object at a time until it is exhausted. Such objects are also called iterable. Python’s for loop processes one constituent of an iterable at a time till it is exhausted. The general form of usage of for statement is as follows:
Example
#using for loop for obj in iterable: #for block #processing instructions of each object . . . end of block
Unlike the while loop, any other Boolean expression is not required to control the repetition of this block. Let us take a simple example. If you want to calculate the square of each number in a list, use for loop as shown below:
Example
#for-1.py numbers=[4,7,2,5,8] for num in numbers: sqr=num*num print ( ' sqaure of { } is { } ' . format ( num , sqr ) )
Output:
E:\python3 7 >python for-1.py square of 4 is 16 square of 7 is 49 square of 2 is 4 square of 5 is 25 square of 8 is 64 E:\python37 >
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Just like a list, a tuple or string object is also iterable. The following code snippet uses a for loop to traverse the characters in a sentence and count the number of words in it assuming that a single space (‘ ‘)separates them.
Example
#for-2.py sentence=1 Simple is better than complex and Complex is. better than complicated. ' wordcount=1 for char in sentence: if char==' ': wordcount=wordcount+1 print ('the sentence has { } words'. format(wordcount))
Output
E:\python37>python for-2.py the sentence has 11 words E:\python37>