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Formulate

Build Status Coverage Status PyPI

Easy conversions between different styles of expressions. Formulate currently supports converting between ROOT and numexpr style expressions.

Installation

Install formulate like any other Python package:

pip install --user formulate

or similar (use `sudo, `virtualenv, or `conda` if you wish).

Usage

Command line usage

$ python -m formulate --from-root '(A && B) || TMath::Sqrt(A)' --to-numexpr
(A & B) | sqrt(A)

$ python -m formulate --from-numexpr '(A & B) | sqrt(A)' --to-root
(A && B) || TMath::Sqrt(A)

$ python -m formulate --from-root '(A && B) || TMath::Sqrt(1.23) * e**1.2 + 5*pi' --variables
A
B

$ python -m formulate --from-root '(A && B) || TMath::Sqrt(1.23) * e**1.2 + 5*pi' --named-constants
E
PI

$ python -m formulate --from-root '(A && B) || TMath::Sqrt(1.23) * e**1.2 + 5*pi' --unnamed-constants
1.2
1.23
5

API

The most basic usage involves calling from_$BACKEND and then to_$BACKEND, for example when starting with a ROOT style expression:

>>> import formulate
>>> momentum = formulate.from_root('TMath::Sqrt(X_PX**2 + X_PY**2 + X_PZ**2)')
>>> momentum
Expression<SQRT>(Expression<ADD>(Expression<POW>(Variable(X_PX), UnnamedConstant(2)), Expression<POW>(Variable(X_PY), UnnamedConstant(2)), Expression<POW>(Variable(X_PZ), UnnamedConstant(2))))
>>> momentum.to_numexpr()
'sqrt(((X_PX ** 2) + (X_PY ** 2) + (X_PZ ** 2)))'
>>> momentum.to_root()
'TMath::Sqrt(((X_PX ** 2) + (X_PY ** 2) + (X_PZ ** 2)))'

Similarly, when starting with a numexpr style expression:

>>> my_selection = formulate.from_numexpr('X_PT > 5 & (Mu_NHits > 3 | Mu_PT > 10)')
>>> my_selection.to_root()
'(X_PT > 5) && ((Mu_NHits > 3) || (Mu_PT > 10))'
>>> my_selection.to_numexpr()
'(X_PT > 5) & ((Mu_NHits > 3) | (Mu_PT > 10))'

If the the type of expression isn't known in advance formulate can also auto detect it:

>>> my_sum = formulate.from_auto('True + False')
>>> my_sum.to_root()
'true + false'
>>> my_sum.to_numexpr()
'True + False'

The Expression Object

When calling from_* the returned object is derived from formulate.ExpressionComponent. From this object you can inspect the expression to find it's dependencies:

>>> my_check = formulate.from_auto('(X_THETA*TMath::DegToRad() > pi/4) && D_PE > 9.2')
>>> my_check.variables
{'D_PE', 'X_THETA'}
>>> my_check.named_constants
{'DEG2RAD', 'PI'}
>>> my_check.unnamed_constants
{'4', '9.2'}

Additionally ExpressionComponent s can be combined using both operators and numpy functions:

>>> new_selection = (momentum > 100) and (my_check or (numpy.sqrt(my_sum) < 1))
>>> new_selection.to_numexpr()
'((X_THETA * 0.017453292519943295) > (3.141592653589793 / 4)) & (D_PE > 9.2)'

As the == operator returns a new expression, it can't be used to check for equality. Instead the .equivalent method should be used:

TODO: Implement this using expression.equivalent !

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