item_18.py

#!/usr/bin/env python3

# Copyright 2014 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.

# Preamble to mimick book environment
import logging
from pprint import pprint
from sys import stdout as STDOUT


# Example 1
def log(message, values):
    if not values:
        print(message)
    else:
        values_str = ', '.join(str(x) for x in values)
        print('%s: %s' % (message, values_str))

log('My numbers are', [1, 2])
log('Hi there', [])


# Example 2
def log(message, *values):  # The only difference
    if not values:
        print(message)
    else:
        values_str = ', '.join(str(x) for x in values)
        print('%s: %s' % (message, values_str))

log('My numbers are', 1, 2)
log('Hi there')  # Much better


# Example 3
favorites = [7, 33, 99]
log('Favorite colors', *favorites)


# Example 4
def my_generator():
    for i in range(10):
        yield i

def my_func(*args):
    print(args)

it = my_generator()
my_func(*it)


# Example 5
def log(sequence, message, *values):
    if not values:
        print('%s: %s' % (sequence, message))
    else:
        values_str = ', '.join(str(x) for x in values)
        print('%s: %s: %s' % (sequence, message, values_str))

log(1, 'Favorites', 7, 33)      # New usage is OK
log('Favorite numbers', 7, 33)  # Old usage breaks