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In general, statements in a program are executed sequentially: The first statement in a function is executed first, followed by the second, and so on. There may be a situation when you need to execute a block of code several number of times. Statements that provide such repetition capability are called looping statements.
In Jython, a loop can be formed by two statements, which are −
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The while statement and
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The for statement
The WHILE Loop
A while loop statement in Jython is similar to that in Java. It repeatedly executes a block of statements as long as a given condition is true. The following flowchart describes the behavior of a while loop.
The general syntax of the while statement is given below.
while expression: statement(s)
The following Jython code uses the while loop to repeatedly increment and print value of a variable until it is less than zero.
count = 0 while count<10: count = count+1 print "count = ",count print "Good Bye!"
Output − The output would be as follows.
count = 1 count = 2 count = 3 count = 4 count = 5 count = 6 count = 7 count = 8 count = 9 count = 10 Good Bye!
The FOR Loop
The FOR loop in Jython is not a counted loop as in Java. Instead, it has the ability to traverse elements in a sequence data type such as string, list or tuple. The general syntax of the FOR statement in Jython is as shown below −
for iterating_var in sequence: statements(s)
We can display each character in a string, as well as each item in a List or Tuple by using the FOR statement as shown below −
#each letter in string for letter in ''Python'': print ''Current Letter :'', letter
Output − The output would be as follows.
Current Letter : P Current Letter : y Current Letter : t Current Letter : h Current Letter : o Current Letter : n
Let us consider another instance as follows.
#each item in list libs = [‘PyQt’, ''WxPython'', ''Tkinter''] for lib in libs: # Second Example print ''Current library :'', lib
Output − The output will be as follows.
Current library : PyQt Current library : WxPython Current library : Tkinter
Here is another instance to consider.
#each item in tuple libs = (‘PyQt’, ''WxPython'', ''Tkinter'') for lib in libs: # Second Example print ''Current library :'', lib
Output − The output of the above program is as follows.
Current library : PyQt Current library : WxPython Current library : Tkinter
In Jython, the for statement is also used to iterate over a list of numbers generated by range() function. The range() function takes following form −
range[([start],stop,[step])
The start and step parameters are 0 and 1 by default. The last number generated is stop step. The FOR statement traverses the list formed by the range() function. For example −
for num in range(5): print num
It produces the following output −
0 1 2 3 4
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