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item_35.py
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#!/usr/bin/env PYTHONHASHSEED=1234 python3
# Copyright 2014-2019 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.
# Reproduce book environment
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)
# Example 1
# create generator "it" call with next method yield values till .throw exception raised
try:
class MyError(Exception):
pass
def my_generator():#yield make func generator object
yield 1
yield 2
yield 3
it = my_generator()#instance of generator
print(next(it)) # Yield 1 call generator once
print(next(it)) # Yield 2 call generator twice
print(it.throw(MyError("test error")))#way to get error by throw method
except:
logging.exception("Expected")
else:
assert False
# Example 2
# first call with next value 1, second call with next value 2 in try block
# third call with next value after yield output value 4 throw error(receive and send part in call for throws exception)
def my_generator():
yield 1#first call
try:
yield 2#second call
except MyError:#thirt is an except because try loop has one value then execpt
print("Got MyError!")
else:
yield 3
yield 4
it = my_generator()#value 1 ,2 can be reached 3 ,4 not with next method on generator
print(next(it)) # Yield 1
print(next(it)) # Yield 2
print(it.throw(MyError("test error")))
# Example 3
class Reset(Exception):
pass
# "timer" generator function counts back to zero
def timer(period):
current = period#assign var with value
while current:#
current -= 1
try:
yield current #after last yield except ->class pass
except Reset:
current = period
print(list(timer(3)))#list calls all yields of generator to list [2, 1, 0]
# Example 4
class Reset(Exception):
pass
RESETS = [
False, # value 3 => 0,1,2,3 timer(4)
False, # value 2 => 0,1,2,3
False, # value 1 => 0,1,2,3
True, # reset to original state value timer 4
False,
True,
False,
False,
False,
False,
False,
False,
False,
False,
]
# if True ok else will deliver False trigger exception pop values from left to right in Reset list
def check_for_reset():
# Poll for external event
return RESETS.pop(0)
# after every item in Reset list announce remaining values timer cycles
def announce(remaining):
print(f"{remaining} ticks remaining")
def run():
it = timer(4) # 0,1,2,3 =>4 times
# while runs loop till exception is raised triggered by RESETS list
while True:
try:
# throw error if RESETS list has True value
if check_for_reset():
current = it.throw(
Reset()
) # call class method as pass and except in timer reset current = period original position
else:
current = next(it)
# if no timer cycles StopIteration exception is raised and break out of loop
except StopIteration:
break
# after every cycle else part of try block returns announce print remaining cycles
else:
announce(current)#will be called every loop ->"3 ticks remaining" etc.
run()
# Example 5
class Timer:#compact class with vars init, reset and iter method we'll use for this exemple
def __init__(self, period):
self.current = period
self.period = period
def reset(self):
self.current = self.period
def __iter__(self):#creates generator
while self.current:
self.current -= 1
yield self.current
# Example 6
RESETS = [
False,
False,
True,
False,
True,
False,
False,
False,
False,
False,
False,
False,
False,
]
def run():
# initialize Timer class =>"timer " variable with 4 cycles
timer = Timer(4)#timer class gives a generator
# loop over timer check RESETS list if True rest, announce per cycle interval
# every event as function in class makes it more obvious
for current in timer:#loop over generator
if check_for_reset(): # check RESETS list very clear false/true in list
timer.reset() # reset timer reset period
announce(current)
run()