If Then Else Statement in Field Calculator using Python - ArcGIS 10.1

Question

I am trying to populate a field [Hazard] based on the values in two other fields [Depth2D] and [Speed2D].

I have managed to write a code block in VB script that works but I really want to figure out how to write it in Python. I cannot seem to get it right.

Underneath is the current iteration of my attempt at python, from what I have seen I need to define the variables to use, but can't seem to define things right.

The VB Script code block is as follows -

Dim hazard

If [DEPTH2D]<0.1 Then
hazard = 1

elseif [DEPTH2D]>=0.1 AND [DEPTH2D]<0.2 AND [SPEED2D]<2 Then
hazard = 2

else
hazard = 3

end if

The Python code block I have tried is as follows

def ifBlock(depth2d,speed2d)

  if: depth2d < 0.1    
         return 1

  elif: depth2d >=0.1 AND depth2d <0.2 AND speed2d<2    
         return 2

  else:
         return 3

I then have

ifBlock([DEPTH2D],[SPEED2D])

in the formula box

The error I am getting in the results window is ERROR999999; Syntax Error

Answer 1

You could define a function with your logic, as in:

def hazLevel(speed, depth):
   if depth < 0.1:
       return 1
   elif (depth < 0.2 and speed < 2):
       return 2
   else:
       return 3

...and in your field calculator form, toward the bottom should be a single line to enter your 'call' the above function (which should be copied to the code logic box. The single line call in this case feeds in the 2 fields for depth and speed:

hazLevel(!Speed2D!, !Depth2D!)

For the Python parser, the '!' delimits the fields...don't forget those, and to tick the Python parser in the field calculator window, as well as maintain proper indentation as shown.

Answer 2

This logic is hard to program, this is why I am using these polygons, where Y is depth and Y is velocity.

Convert relevant fields data into points, accordingly and do a spatial join to above polygons to calculate hazard