Professional IronPython

LISTINg 3-6: 
 Looping through data using while
# Create an array of strings.
MyList = ‘Hello’, ‘Goodbye’, ‘Red’, ‘Green’
# Define a counter variable.
Counter = 0
# Define the current string.
ThisString = ‘’
# Process the array. 
while ThisString != ‘Green’:
# Get the next value.
ThisString = MyList[Counter]
# Display the individual values.
print ‘The current value is:’, ThisString
# Update the counter.
Counter+=1
# Pause after the debug session.
raw_input(‘Press any key to continue...’)
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2/24/10 12:47:30 PM
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Performing Enumerations
 
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53
This example begins with the same array as shown in Listing 3-5. In order to make the 
while
loop 
work, the code must define 
Counter
, which keeps track of the current array element. The code also 
defines 
ThisString
, which holds the current array value. As you can already see, the 
while
loop 
isn’t nearly as automatic as the 
for...in
loop, but it does provide considerable flexibility.
In this case, the 
while
loop continues to run until 
ThisString
is equal to 
‘Green‘
, the last value in 
the array. As always, the 
while
statement ends with a colon and every indented statement after it is 
part of the 
while
structure.
The code relies on 
Counter
to access the individual array elements. You simply provide Counter as an 
index into 
MyList
using 
MyList[Counter]
. The code then prints out the value found in 
ThisString
. 
Finally, the code updates Counter. Notice that IronPython supports the use of the 
+=
shortcut. The out-
put from this application appears in Figure 3-4.
FIgURE 3-4: 
Use the while loop when you need to perform tasks an indeterminate number of times.
You might have noticed that IronPython doesn’t appear to support the vast array 
of loop statement subsets found in other languages. For example, there isn’t any 
version of the 
while
 statement that tests for the condition after executing the code 
the first time. In general, this apparent limitation actually makes things consider-
ably easier. You simply need to write your code in such a way as to accommodate 
the “test first” orientation of the IronPython 
while
 loop.