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Calculator App handles fractions natively using Python’s built-in fractions.Fraction class, which stores rational numbers as exact numerator/denominator pairs. This means operations like 1/2 + 1/3 return the mathematically exact result 5/6 rather than an approximation like 0.8333333333333333.

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How Fraction Parsing Works

The parse_fractions() function in fractions.py scans the input expression for fraction patterns using regular expressions and converts them into Fraction(numerator, denominator) calls before the expression is passed to eval.

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Simple Fractions

A simple fraction like a/b is matched by: 
expr = re.sub(r'(\d+)/(\d+)', fraction_replacer, expr)
# e.g. "1/2" → "Fraction(1, 2)"

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Mixed Fractions

A mixed number like whole num/den (e.g., 2 1/2) is matched first — before simple fractions — to avoid double-replacing: 
expr = re.sub(r'(\d+)\s+(\d+)/(\d+)', mixed_fraction_replacer, expr)
# e.g. "2 1/2" → "Fraction(5, 2)"  (because 2*2 + 1 = 5)
The whole number is converted to an improper numerator: whole * denominator + numerator.

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Output Formatting

After evaluation, the result is a Fraction object. The calc() function in evaluator.py formats it according to these rules:
1

Denominator is 1

Returns the integer value directly — e.g., Fraction(4, 1) → 4.
2

Improper fraction

Converts to mixed number form — e.g., Fraction(13, 4) → 3 1/4.
3

Proper fraction

Returns numerator/denominator — e.g., Fraction(5, 6) → 5/6.

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Examples

> 1/2 + 1/3
= 5/6

> 3/4 - 1/4
= 1/2

> 2 1/2 + 1/4
= 2 3/4

> 1/2 * 2
= 1

> 2 1/2 + 3/4
= 3 1/4

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Combining Fractions with Other Operations

Fractions can be freely combined with integers, decimals, and other operations. For example, 1/2 * 6 + 3/4 evaluates all terms with exact rational arithmetic before returning the result.
> 1/2 * 6
= 3

> 3/4 + 1
= 1 3/4

> 2 1/2 * 2
= 5

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Under the Hood

The Fraction class is included in the safe_dict passed to eval, so the converted expressions like Fraction(1, 2) + Fraction(1, 3) execute safely within the restricted evaluation environment. 
safe_dict = {
    '__builtins__': {},
    'Fraction': Fraction,
    # ... other functions
}

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