Fractional math (token based)
Summary
This is includes a source transformation that converts
integers literals that are followed by the / operator
into instances of the Fraction class in the source using the tokenizer.
In a later section, we do something similar but using an Abstract Syntax Tree (AST) transformation, which is a more robust approach for this type of example.
Consider the following standard Python code:
>>> x = 1/10
>>> for i in range(11):
... print(i * x)
...
0.0
0.1
0.2
0.30000000000000004
0.4
0.5
0.6000000000000001
0.7000000000000001
0.8
0.9
1.0
This is quite surprising for beginners, not familiar with the limitations of representing floating point numbers.
However, we can “fix” this using an import hook that wraps
integer, which are followed by a /, into a Fraction instance:
> python -m ideas -a fractions_tok
The following initializing code from ideas is included:
from fractions import Fraction
Ideas Console version 0.0.38. [Python version: 3.7.9]
ideas> x = 1 / 10
ideas> for i in range(11):
... print(i * x)
...
0
1/10
1/5
3/10
2/5
1/2
3/5
7/10
4/5
9/10
1
ideas> from ideas.session import config
ideas> config.show_changes = True
ideas> x = 1 / 10
new: x = Fraction(1) / 10
ideas>
This example was created after a similar example using AST transformation was created as a proof of concept. For more details about the difference, please have a look at the AST-based example.
- ideas.examples.fractions_tok.add_hook(**_kwargs)[source]
Creates and automatically adds the import hook in sys.meta_path.