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item_22.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
# make log from message and join statement with tuple comprehension
# with no values TypeError missing values
def log(message, values):
if not values:
print(message)
else:
values_str = ", ".join(str(x) for x in values)
print(f"{message}: {values_str}")
log("My numbers are", [1, 2])
log("Hi there", [])#test empty list []->False
log("Hi there2")#should 2 args now error
# Example 2
# use " * " before variable to declare variable optional
# no values gives "()" => not () evaluates to true
def log(message, *values): # The only difference -> values is optional
if not values:
print(message)
print(values)
else:
values_str = ", ".join(str(x) for x in values)
print(f"{message}: {values_str}")
log("My numbers are", 1, 2)
log("Hi there") # Much better no error *arg makes values optional
# Example 3
# receive list as seperate items after message not as 1 list
favorites = [7, 33, 99]
log("Favorite colors", *favorites)#takes even list values as multiple argument use as seperate item from list
log("Favorite colors", favorites)#now arg is the list as item
# Example 4
def my_generator():
for i in range(10):
yield i#optional without works
def my_func(*args):
print(args)
# with unpack you need a variable and *variable
# this you assign generator to a variable it and print *it
it = my_generator()
print(*it)#print all items by *var
print(it)#print object
# here unpack first then print a,it
a, *it = my_generator()
print([a, it])#prints list with 2items a and list it
# print trough function double *variable
it = my_generator()#call func return items
my_func(*it)#use items in func
my_func(it)#gets generator object
# Example 5
def log(sequence, message, *values):
# when values is empty tuple () => not () is True them no values printed
if not values:
print(f"{sequence} - {message}")
# if values print all
else:
values_str = ", ".join(str(x) for x in values)
print(f"{sequence} - {message} {values_str}")
log(1, "Favorites", 7, 33) # New with *args OK "1 - Favorites 7, 33"
log(1, "Hi there") # New message only OK "1 - Hi there"
log("Favorite numbers", 7, 33) # Old usage breaks#now value message can be the first number "Favorite numbers - 7 33"