actually commit TP2

TP02/python/type_unions.py

@@ -0,0 +1,52 @@
+from typing import List
+
+# int | float means ``either an int or a float''.
+NUMBER = int | float  # or Union[int, float] with Union imported from typing
+
+
+def add_numbers(a: NUMBER, b: NUMBER) -> NUMBER:
+    return a + b
+
+
+# Both int and floats can be passed to the function
+print(add_numbers(1, 4.3))
+
+
+def divide_numbers(a: NUMBER, b: NUMBER) -> float:
+    return a / b
+
+
+print(divide_numbers(1, 2))
+
+# Declare the type of a list whose elements are numbers.
+LIST_OF_NUMBERS = List[NUMBER]
+
+
+def increment(a: LIST_OF_NUMBERS) -> LIST_OF_NUMBERS:
+    return [x + 1 for x in a]
+
+
+print(increment([1, 2, 3]))
+
+# Skip the end if you are late.
+
+# The type DEEP_LIST_OF_NUMBERS is a special case since it references itself.
+# The identifier DEEP_LIST_OF_NUMBERS cannot be used before the end of its
+# initialization, but the circular dependency can be broken using the string
+# 'DEEP_LIST_OF_NUMBERS' instead.
+DEEP_LIST_OF_NUMBERS = NUMBER | List['DEEP_LIST_OF_NUMBERS']
+
+
+def deep_increment(d: DEEP_LIST_OF_NUMBERS) -> DEEP_LIST_OF_NUMBERS:
+    if isinstance(d, list):
+        # Note the unusual typing rule applied by Pyright here: because we are
+        # in the 'isinstance(d, list)' branch, it knows that d is a list,
+        # and accepts to iterate over it.
+        return [deep_increment(e) for e in d]
+    else:
+        # ... and here, in the 'else' branch Pyright knows that d is not a list,
+        # and can deduce that it is a NUMBER.
+        return d + 1
+
+
+print(deep_increment([1, [2, 3]]))

TP02/python/typecheck.py

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+# Typing annotations for variables:
+# name: type
+int_variable: int
+float_variable: float
+int_variable = 4.2  # Static typing error, but no runtime error
+float_variable = 42.0  # OK
+float_variable = int_variable  # OK
+
+
+# Typing annotations for functions (-> means "returns")
+def int_to_string(i: int) -> str:
+    return str(i)
+
+
+print(int_to_string('Hello'))  # Static typing error, but no runtime error
+print(int_to_string(42) / 5)  # Both static and runtime error