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# Exercise 2 SolutionsΒΆ

The aim of this exercise is to write a small Python algorithm that is able
to print to the Messages Box the first `n`

numbers of the Fibonacci series.
The series starts with `0, 1`

and then the next term is the sum of the
two previous terms.

```
# Extending Mantid With Python: Exercise 2
#
# The algorithm should:
# - Define a property that sets the maximum number of terms to print. Single letters are not considered good property names so a good name
# would be something like NTerms
# - The property should have documentation that shows in the GUI describing what it is used for.
# - Validate that NTerms property is greater or equal to 1 when set in the GUI.
# - The log message for the value of each term should be at notice level and in the format: "Term 1 in the Fibonacci series is: 0"
# - Add log message at debug level that prints the value of the NTerms property after it has been retrieved.
#
# As an additional exercise in understanding errors:
# - On execution, check that the value of NTerms is less than or equal to 1000. If it is not then raise a RuntimeError.
from mantid.kernel import *
from mantid.api import *
class FibonacciExercise(PythonAlgorithm):
def category(self):
return "Examples"
def PyInit(self):
self.declareProperty(name="NTerms", defaultValue=-1, validator=IntBoundedValidator(lower=0), doc="Number of terms to print")
def PyExec(self):
nterms = self.getProperty("NTerms").value
self.log().debug("NTerms = " + str(nterms))
if nterms > 1000:
raise RuntimeError("Number of terms greater than 1000")
# 0 should print something else
if nterms < 1:
msg = "Number of terms selected less than 1"
else:
# First two terms
prev_2, prev_1 = 0, 1
msg = "Term 1 in the Fibonacci series is: " + str(prev_2) + "\n"
msg += "Term 2 in the Fibonacci series is: " + str(prev_1) + "\n"
count = 2
while count < nterms:
count += 1
current = prev_2 + prev_1
msg += "Term " + str(count) + " in the Fibonacci series is: " + str(current) + "\n"
prev_2 = prev_1
prev_1 = current
# End of else
# Display whole log message in single shot
self.log().notice(msg)
# Register algorithm with mantid
AlgorithmFactory.subscribe(FibonacciExercise)
```