Unit Conversion in Python
Convert units programmatically in Python using pint, dimensionless, and built-in math — with examples.
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Tags: unit conversion Python, Python pint library, Python unit calculator
Unit Conversion in Python Python has two main approaches to unit conversion: manual constants (fast, simple) and the library (type-safe, powerful). Choosing between them depends on whether you need dimensional safety and user-defined units, or just need to convert a fixed set of quantities. --- Approach 1: Manual Conversion Constants For fixed, well-known conversions, explicit constants are the simplest and fastest approach: Strengths: Zero dependencies, fast, easy to read. Weaknesses: No dimensional safety — adding metres to kilograms silently produces wrong results. Approach 2: The pint Library attaches physical units to numbers and enforces dimensional consistency: Temperature Conversion with pint Temperature is special in pint because Celsius and Fahrenheit are offset scales, not…
Frequently Asked Questions
What is the pint library for unit conversion?
Pint is a Python library that defines units, quantities, and unit registries. It lets you attach units to numbers, perform unit-aware arithmetic, and convert between compatible units. Install with pip install pint. It raises DimensionalityError when you try to add incompatible units, preventing silent bugs.
How do I convert units in Python without a library?
Define conversion factors as constants and multiply: METERS_TO_FEET = 3.28084; feet = meters * METERS_TO_FEET. For temperature: fahrenheit = celsius * 9/5 + 32. This is fine for simple, static conversions. Use pint when you need dimensional safety or user-specified unit strings.
How do I handle unit conversion errors in Python?
With pint, catch pint.DimensionalityError for incompatible units and pint.UndefinedUnitError for unknown unit names. For manual conversions, validate inputs: check that values are numeric, non-negative (for absolute quantities), and within reasonable bounds.
How do I convert temperatures in Python?
Without pint: C_to_F = lambda c: c * 9/5 + 32. With pint: temp = ureg.Quantity(100, 'degC'); temp.to('degF') returns 212 degF. Note that pint requires 'degC' not 'celsius' and handles the offset-based conversion correctly.
Can Python handle physical units in equations?
Yes, pint handles full dimensional analysis. Multiplying distance (metres) by time (seconds) gives m·s, not a float. You can define custom units, convert compound units, and use pint.Quantity in numpy arrays for vectorized unit-safe operations.
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