Fix: Cached Property support for Python 3.6 and 3.7

rocketpy/Flight.py

@@ -9,7 +9,6 @@
 import math
 import time
 import warnings
-from functools import cached_property
 
 import matplotlib.pyplot as plt
 import numpy as np
@@ -18,6 +17,11 @@
 
 from .Function import Function
 
+try:
+    from functools import cached_property
+except ImportError:
+    from .tools import cached_property
+
 
 class Flight:
     """Keeps all flight information and has a method to simulate flight.

rocketpy/tools.py

@@ -0,0 +1,25 @@
+_NOT_FOUND = object()
+
+
+class cached_property:
+    def __init__(self, func):
+        self.func = func
+        self.attrname = None
+        self.__doc__ = func.__doc__
+
+    def __set_name__(self, owner, name):
+        self.attrname = name
+
+    def __get__(self, instance, owner=None):
+        if instance is None:
+            return self
+        if self.attrname is None:
+            raise TypeError(
+                "Cannot use cached_property instance without calling __set_name__ on it."
+            )
+        cache = instance.__dict__
+        val = cache.get(self.attrname, _NOT_FOUND)
+        if val is _NOT_FOUND:
+            val = self.func(instance)
+            cache[self.attrname] = val
+        return val