`xoutil.fp.prove` - Prove validity of values

Proving success or failure of a function call has two main patterns:

Predicative: a function call returns one or more values indicating a failure, for example method find in strings returns -1 if the sub-string is not found. In general this pattern considers a set of values as logical Boolean true, an other set false.

Example:
```
index = s.find('x')
if index >= 0:
    ...    # condition of success
else:
    ...    # condition of failure
```
Disruptive: a function call throws an exception on a failure breaking the normal flow of execution, for example method index in strings.

Example:
```
try:
    index = s.index('x)
except ValueError:
    ...    # condition of failure
else:
    ...    # condition of success
```
The exception object contains the semantics of the ""anomalous condition". Exception handling can be used as flow control structures for execution context inter-layer processing, or as a termination condition.

Module content

xoutil.fp.prove