ch08, 09, 10: example files

Author: ramalho

08-def-type-hints/README.asciidoc

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+== Type Hints in Function Definitions

08-def-type-hints/RPN_calc/calc.py

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+#!/usr/bin/env python3
+
+import sys
+from array import array
+from typing import Mapping, MutableSequence, Callable, Iterable, Sequence, Union, Any
+
+
+OPERATORS: Mapping[str, Callable[[float, float], float]] = {
+    '+': lambda a, b: a + b,
+    '-': lambda a, b: a - b,
+    '*': lambda a, b: a * b,
+    '/': lambda a, b: a / b,
+    '^': lambda a, b: a ** b,
+}
+
+
+Stack = MutableSequence[float]
+
+
+def parse_token(token: str) -> Union[str, float]:
+    try:
+        return float(token)
+    except ValueError:
+        return token
+
+
+def evaluate(tokens: Iterable[str], stack: Stack) -> None:
+    for token in tokens:
+        atom = parse_token(token)
+        if isinstance(atom, float):
+            stack.append(atom)
+        else:  # not float, must be operator
+            op = OPERATORS[atom]
+            x, y = stack.pop(), stack.pop()
+            result = op(y, x)
+            stack.append(result)
+
+
+def display(s: Stack) -> str:
+    items = (repr(n) for n in s)
+    return ' │ '.join(items) + ' →'
+
+
+def repl(input_fn: Callable[[Any], str] = input) -> None:
+    """Read-Eval-Print-Loop"""
+
+    print('Use CTRL+C to quit.', file=sys.stderr)
+    stack: Stack = array('d')
+
+    while True:
+        try:
+            line = input_fn('> ')              # Read
+        except (EOFError, KeyboardInterrupt):
+            break
+        try:
+            evaluate(line.split(), stack)      # Eval
+        except IndexError:
+            print('*** Not enough arguments.', file=sys.stderr)
+        except KeyError as exc:
+            print('*** Unknown operator:', exc.args[0], file=sys.stderr)
+        print(display(stack))                  # Print
+
+    print()
+
+
+if __name__ == '__main__':
+    repl()