item_05.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
a = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']
print('First four:', a[:4])
print('Last four: ', a[-4:])
print('Middle two:', a[3:-3])


# Example 2
assert a[:5] == a[0:5]


# Example 3
assert a[5:] == a[5:len(a)]


# Example 4
print(a[:5])
print(a[:-1])
print(a[4:])
print(a[-3:])
print(a[2:5])
print(a[2:-1])
print(a[-3:-1])


# Example 5
a[:]      # ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']
a[:5]     # ['a', 'b', 'c', 'd', 'e']
a[:-1]    # ['a', 'b', 'c', 'd', 'e', 'f', 'g']
a[4:]     #                     ['e', 'f', 'g', 'h']
a[-3:]    #                          ['f', 'g', 'h']
a[2:5]    #           ['c', 'd', 'e']
a[2:-1]   #           ['c', 'd', 'e', 'f', 'g']
a[-3:-1]  #                          ['f', 'g']


# Example 6
first_twenty_items = a[:20]
last_twenty_items = a[-20:]


# Example 7
try:
    a[20]
except:
    logging.exception('Expected')
else:
    assert False


# Example 8
b = a[4:]
print('Before:   ', b)
b[1] = 99
print('After:    ', b)
print('No change:', a)


# Example 9
print('Before ', a)
a[2:7] = [99, 22, 14]
print('After  ', a)


# Example 10
b = a[:]
assert b == a and b is not a


# Example 11
b = a
print('Before', a)
a[:] = [101, 102, 103]
assert a is b           # Still the same list object
print('After ', a)      # Now has different contents