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item_047.py
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executable file
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#!/usr/bin/env PYTHONHASHSEED=1234 python3
# Copyright 2014-2024 Brett Slatkin, Pearson Education Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
### Start book environment setup
import random
random.seed(1234)
import logging
from pprint import pprint
from sys import stdout as STDOUT
# Write all output to a temporary directory
import atexit
import gc
import io
import os
import tempfile
TEST_DIR = tempfile.TemporaryDirectory()
atexit.register(TEST_DIR.cleanup)
# Make sure Windows processes exit cleanly
OLD_CWD = os.getcwd()
atexit.register(lambda: os.chdir(OLD_CWD))
os.chdir(TEST_DIR.name)
def close_open_files():
everything = gc.get_objects()
for obj in everything:
if isinstance(obj, io.IOBase):
obj.close()
atexit.register(close_open_files)
### End book environment setup
print("Example 1")
try:
class MyError(Exception):
pass
def my_generator():
yield 1
yield 2
yield 3
it = my_generator()
print(next(it)) # Yields 1
print(next(it)) # Yields 2
print(it.throw(MyError("test error"))) # Raises
except:
logging.exception('Expected')
else:
assert False
print("Example 2")
def my_generator():
yield 1
try:
yield 2
except MyError:
print("Got MyError!")
else:
yield 3
yield 4
it = my_generator()
print(next(it)) # Yields 1
print(next(it)) # Yields 2
print(it.throw(MyError("test error"))) # Yields 4
print("Example 3")
class Reset(Exception):
pass
def timer(period):
current = period
while current:
try:
yield current
except Reset:
print("Resetting")
current = period
else:
current -= 1
print("Example 4")
ORIGINAL_RESETS = [
False,
False,
False,
True,
False,
True,
False,
False,
False,
False,
False,
False,
False,
False,
]
RESETS = ORIGINAL_RESETS[:]
def check_for_reset():
# Poll for external event
return RESETS.pop(0)
def announce(remaining):
print(f"{remaining} ticks remaining")
def run():
it = timer(4)
while True:
try:
if check_for_reset():
current = it.throw(Reset())
else:
current = next(it)
except StopIteration:
break
else:
announce(current)
run()
print("Example 5")
class Timer:
def __init__(self, period):
self.current = period
self.period = period
def reset(self):
print("Resetting")
self.current = self.period
def tick(self):
before = self.current
self.current -= 1
return before
def __bool__(self):
return self.current > 0
print("Example 6")
RESETS = ORIGINAL_RESETS[:]
def run():
timer = Timer(4)
while timer:
if check_for_reset():
timer.reset()
announce(timer.tick())
run()