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pythonjinja2

import python libraries in jinja2 templates

I have this template:

% template.tmpl file:
% set result = fractions.Fraction(a*d + b*c, b*d) %}
The solution of ${{a}}/{{b}} + {{c}}/{{d}}$ is ${{a * d + b*c}}/{{b*d}} = {{result.numerator}}/{{result.denominator}}$

which I invoke by

from jinja2 import Template
import fractions

with open("c.jinja") as f:
    t = Template(f.read())
    a = 2
    b = 3
    c = 4
    d = 5
    print(t.render(a = a, b = b, c=c, d=d))

I get

jinja2.exceptions.UndefinedError: 'fractions' is undefined

but I want

The solution of $2/3 + 4/5$ is $22/15=22/15$.

Is this possible to achieve that?

Solution

  • It can be done in two ways.

    1. Calculate the result in Python code and then pass it as a parameter to the template.
    2. You can pass the fractions module as a parameter to the template.

    Folder structure:

    .
├── c.jinja
└── template_example.py

    Option 1: Pass result to the template:

    template_example.py:

    from jinja2 import Template
import fractions

with open("c.jinja") as f:
    t = Template(f.read())
    a = 2
    b = 3
    c = 4
    d = 5
    result = fractions.Fraction(a * d + b * c, b * d)
    print(t.render(a=a, b=b, c=c, d=d, result=result))

    c.jinja:

    The solution of ${{a}}/{{b}} + {{c}}/{{d}}$ is ${{a * d + b*c}}/{{b*d}} = {{result.numerator}}/{{result.denominator}}$

    Option 2: Pass the fractions:

    template_example.py:

    from jinja2 import Template
import fractions

with open("c.jinja") as f:
    t = Template(f.read())
    a = 2
    b = 3
    c = 4
    d = 5
    print(t.render(a=a, b=b, c=c, d=d, fractions=fractions))

    c.jinja:

    {% set result = fractions.Fraction(a*d + b*c, b*d) %}
The solution of ${{a}}/{{b}} + {{c}}/{{d}}$ is ${{a * d + b*c}}/{{b*d}} = {{result.numerator}}/{{result.denominator}}$

    Output for both options:

    The solution of $2/3 + 4/5$ is $22/15 = 22/15$

    I would recommend Option 1: Pass the result to the template. This approach keeps the template focused on its primary role: rendering text with provided data, while the Python code handles all the computations.