Python constants: code examples (#275)

* Python constants: code examples

* Fix linter issues

* More linter issues

* Add a README.md file

* Final QA updates

Co-authored-by: Geir Arne Hjelle <[email protected]>

Author: lpozo

python-constants/README.md

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+# Python Constants: Improve Your Code's Maintainability
+
+This folder provides the code examples for the article [Python Constants: Improve Your Code's Maintainability](https://realpython.com/python-constants/).

python-constants/calculations/calc/__init__.py

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+# calculations.py
+
+"""This module implements custom calculations."""
+
+# Imports go here...
+# import numpy as np
+
+from . import constants
+
+
+# Your custom calculations start here...
+def circular_land_area(radius):
+    return constants.PI * radius**2
+
+
+def future_value(present_value, interest_rate, years):
+    return present_value * constants.EULER_NUMBER ** (interest_rate * years)

python-constants/calculations/calc/calculations.py

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+# constants.py
+
+"""This module defines project-level constants."""
+
+PI = 3.141592653589793
+EULER_NUMBER = 2.718281828459045
+TAU = 6.283185307179586

python-constants/calculations/calc/constants.py

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+# calculations1.py
+
+"""This module implements custom calculations."""
+
+# Imports go here...
+# import numpy as np
+
+# Constants go here...
+PI = 3.141592653589793
+EULER_NUMBER = 2.718281828459045
+TAU = 6.283185307179586
+
+
+# Your custom calculations start here...
+def circular_land_area(radius):
+    return PI * radius**2
+
+
+def future_value(present_value, interest_rate, years):
+    return present_value * EULER_NUMBER ** (interest_rate * years)
+
+
+# ...

python-constants/calculations/calculations1.py

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+# calculations3.py
+
+"""This module implements custom calculations."""
+
+# Imports go here...
+from configparser import ConfigParser
+
+# import numpy as np
+
+constants = ConfigParser()
+constants.read("path/to/constants.ini")
+
+
+# Your custom calculations start here...
+def circular_land_area(radius):
+    return float(constants.get("CONSTANTS", "PI")) * radius**2
+
+
+def future_value(present_value, interest_rate, years):
+    return (
+        present_value * float(constants.get("CONSTANTS", "EULER_NUMBER"))
+    ) ** (interest_rate * years)
+
+
+# ...

python-constants/calculations/calculations3.py

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+; constants.ini
+
+[CONSTANTS]
+PI=3.141592653589793
+EULER_NUMBER=2.718281828459045
+TAU=6.283185307179586

python-constants/calculations/constants.ini

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+# circle1.py
+
+
+class Circle:
+    def __init__(self, radius):
+        self.radius = radius
+
+    def area(self):
+        return 3.14 * self.radius**2
+
+    def perimeter(self):
+        return 2 * 3.14 * self.radius
+
+    def projected_volume(self):
+        return 4 / 3 * 3.14 * self.radius**3
+
+    def __repr__(self):
+        return f"{self.__class__.__name__}(radius={self.radius})"

python-constants/circle1.py

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+# circle2.py
+
+PI = 3.14
+
+
+class Circle:
+    def __init__(self, radius):
+        self.radius = radius
+
+    def area(self):
+        return PI * self.radius**2
+
+    def perimeter(self):
+        return 2 * PI * self.radius
+
+    def projected_volume(self):
+        return 4 / 3 * PI * self.radius**3
+
+    def __repr__(self):
+        return f"{self.__class__.__name__}(radius={self.radius})"

python-constants/circle2.py

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+# circle3.py
+
+import math
+
+
+class Circle:
+    def __init__(self, radius):
+        self.radius = radius
+
+    def area(self):
+        return math.pi * self.radius**2
+
+    def perimeter(self):
+        return 2 * math.pi * self.radius
+
+    def projected_volume(self):
+        return 4 / 3 * math.pi * self.radius**3
+
+    def __repr__(self):
+        return f"{self.__class__.__name__}(radius={self.radius})"