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item_11.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
a = ["a", "b", "c", "d", "e", "f", "g", "h"]
print("Middle two: ", a[3:5]) #3=>fourth item
print("All but ends:", a[1:7])
# Example 2
# list tot 5 =>0,1,2,3,4
assert a[:5] == a[0:5]
print(a[:5], "==", a[0:5])
# Example 3
# from item 6,7,8 pos 6 is included
assert a[5:] == a[5 : len(a)]
print(a[5:], " ==", a[5 : len(a)])#len(a) geeft lengte list aan
# Example 4
# a = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']
print(a[:]) # all items
print(a[:5]) # till pos 6 a-e
print(a[:-1]) # a-g last item not included
print(a[4:]) # e-h 5e pos included
print(a[-3:]) # f-h 3e from end incl
print(a[2:5]) # pos 3 till 6 =>c-e (f not included)
print(a[2:-1]) # 3e pos till 1e from end (c-g)
print(a[-3:-1]) # 3e pos from end till 1e from end (f-g)
# Example 5
# see exemp 4
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
# means all list shorter then 20 items
first_twenty_items = a[:20]#till pos 20
print(first_twenty_items)
# means all list shorter then 20 items
last_twenty_items = a[-20:]#from end the 20 pos back
print(last_twenty_items)
# Example 7
# item 20 doesn't exist in the list
try:
a[20]#list has 8 pos
except:
logging.exception("Expected")
else:
assert False
# Example 8
# a = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']
b = a[3:]#assign part a to list b
print("Before: ", b) # d-h
b[1] = 99 #assign 99 to pos 2
print("After: ", b) # 2 pos is 99
print("No change:", a) # all
# Example 9
# replace part of list with new list
print("Before ", a)
a[2:7] = [99, 22, 14] # 3 pos till pos 8 => c-g = 99,22,14 even diiferent format replace
print("After ", a)
# Example 10
# Before ['a', 'b', 99, 22, 14, 'h']
print("Before ", a)
a[2:3] = [47, 11] # pos 3 => 47,11
# 99 is now 47,11
print("After ", a) #even 1 pos replace by 2
# Example 11
# a[:] assign a copy to b values are the same but a and are not identical.
# not same reference to objects with a = b values and ref is the same
b = a[:] # b gets copy of a values are the same reference not
print(b)
print(a)
assert b == a and b is not a # True(same values => ==) and True(not same ref/object =>is not)
print(b == a, "and", b is not a)
print(id(a) == id(b))
print(id(a) is id(b))
print(id(a))
print(id(b))
# Example 12
b = a #assign value a to b
print(id(a) == id(b))#value of the id's is the same
print(id(a) is id(b))
print("Before a", a)
print("Before b", b)
assert b == a and b is not a #
print(b == a, "and", b is not a)#value referenced by a and b is the same => '==' , but is another name/object => is/is not
print(id(a) == id(b))#a and b have another id number
print(id(a)) #a and b have same object id number
print(id(b))
a[:] = [101, 102, 103]
print(b)#b point to a
print(a)
print(id(a) == id(b)) #same id'd
assert a is b # Still the same list object referend by a and b
print("After a ", a) # Now has different contents
print("After b ", b) # Same list, so same contents as a
assert b == a and b is not a
assert b is not a
print(b == a, "and", b is not a)
print(id(a) == id(b))