# Have a short convenience method to get probability of truth

Issue #23 closed
Pierre Denis
repo owner created an issue

By default, Lea does not display individual probabilities but probability distributions; this is so even for boolean variables (i.e. probability of False and probability of True). For boolean variables, it's very common and natural to require only the probability of True, as a fraction or float. Lea provides general methods to do that: `p` (fraction) and `pmf` (float):

```>>> rain = Lea.boolProb(1,4)
>>> rain.p(True)
1/4
>>> rain.pmf(True)
0.25
>>> die = Lea.interval(1,6)
>>> ((2 <= die) & (die < 6)).p(True)
2/3
>>> ((2 <= die) & (die < 6)).pmf(True)
0.6666666666666666
```

It would be nice to allow for a shorter, handy, syntax, that avoids the `True` argument. The following is suggested (note the capital `P` to avoid confusion with `p` method):

```>>> rain.P
1/4
>>> rain.Pf
0.25
>>> ((2 <= die) & (die < 6)).P
2/3
>>> ((2 <= die) & (die < 6)).Pf
0.6666666666666666
```

Also, these methods could be provided as pure functions, enabling a syntax close to standard mathematical notations:

```>>> P(rain)
1/4
>>> Pf(rain)
0.25
>>> P((2 <= die) & (die < 6))
2/3
>>> Pf((2 <= die) & (die < 6))
0.6666666666666666
```

Syntactic sugar matters!