#  Python 3
#  Author: Jonathan Goodman, goodman@cims.nyu.edu
#  Fall 2024
#  for the class Scientific Computing
#  https://math.nyu.edu/~goodman/teaching/ScientificComputing2024/ScientificComputing.html

#  Illustrate a function reporting failure and the calling code dealing
#  with it.

# This file: exceptionDemo.py,

import numpy as np

#     return the NaN generated by np.sqrt if x < 0 -- creates a mess

def myRootNaN(x):           # return NaN if x is negative
   return np.sqrt(x)        # makes NaN if x<0, but also raises an error flag.
                            # Either turn off the error flag or use the ...
                            # ... myRootNone(x) function below.
                            
#     test for x<0 and return None if it is.  Clean result.

def myRootNone(x):           # Return None if x is negative
   if x >= 0.:
      return np.sqrt(x)
   else:
      return None           # This reports failure
      
#     test for x<0 and raise an exception if it is.  The official method.
                            
class NegativeArgument(Exception):  # Create a named excdeption.  This ...
    pass                            # .. exception class exists but does nothing
    
def myRootExcept(x):
   if x < 0.:
      raise NegativeArgument()      # This reports failure
   else:
      return np.sqrt(x)
      
xValues = [4, 3., 0., -2.]       # test numbers

print("\n    The Nan version:")
for x in xValues:
   y = myRootNaN(x)
   if np.isnan(y):
      outLine = "The number x = {x:7.2f} does not have a square root"
      outLine = outLine.format(x=x)
   else:
      outLine = "The square root of {x:7.2f} is {y:8.3f}"
      outLine = outLine.format(x=x, y=y)
   print(outLine)

print("\n    The None version:")
for x in xValues:
   y = myRootNone(x)
   if (y != None):
      outLine = "The square root of {x:7.2f} is {y:8.3f}"
      outLine = outLine.format(x=x, y=y)
   else:
      outLine = "The number x = {x:7.2f} does not have a square root"
      outLine = outLine.format(x=x)
   print(outLine)
   
print("\n    The Try, Except, Else, Finally version:")
for x in xValues:
   try:
      y = myRootExcept(x)
   except NegativeArgument:
      outLine = "The number x = {x:7.2f} does not have a square root"
      outLine = outLine.format(x=x)
   else:
      outLine = "The square root of {x:7.2f} is {y:8.3f}"
      outLine = outLine.format(x=x,y=y)
   finally:
      print(outLine)
   
""" (three quotes start and end a multi-line comment)
Should produce:
   The square root of    4.00 is    2.000
   The square root of    3.00 is    1.732
   The square root of    0.00 is    0.000
   The number x =   -2.00 does not have a square root
"""