3.7.0 (v3.7.0:1bf9cc5093, Jun 26 2018, 23:26:24) 
[Clang 6.0 (clang-600.0.57)]
Python Type "help", "copyright", "credits" or "license" for more information.
# More on lists

l1 = [1, 2, 3]
l1[0]
1
l2 = l1
l2
[1, 2, 3]
id(l1)
4522708488
id(l2)
4522708488
# lists are mutable
# mutable == changeable 
# we can change the contents of the list without changing its
# memory address
help(list.append)
Help on method_descriptor:

append(self, object, /)
    Append object to the end of the list.

l1.append('cat')
l1
[1, 2, 3, 'cat']
id(l1)
4522708488
l2
[1, 2, 3, 'cat']
id(l2)
4522708488
# since l1 and l2 both have the same memory address, when we add to one
# list, we add to the other 
# the method list.append does not create a new list with a new 
# memory address, it just 'edits' the list in place
# It keeps the same memory address

# List methods that mutate (change) lists
help(list.append)
Help on method_descriptor:

append(self, object, /)
    Append object to the end of the list.

help(list.insert)
Help on method_descriptor:

insert(self, index, object, /)
    Insert object before index.

L = [1, 2, 3, 4]
L.insert(2, 5)
L
[1, 2, 5, 3, 4]
id(L)
4522578120
L.insert(len(L), 5)
L
[1, 2, 5, 3, 4, 5]
id(L)
4522578120
K = L
K.insert(len(L), 7)
K
[1, 2, 5, 3, 4, 5, 7]
L
[1, 2, 5, 3, 4, 5, 7]
id(K)
4522578120
id(L)
4522578120
help(list.sort)
Help on method_descriptor:

sort(self, /, *, key=None, reverse=False)
    Stable sort *IN PLACE*.

L.sort()
L
[1, 2, 3, 4, 5, 5, 7]
# also sorts in place - memory address doesn't change
K
[1, 2, 3, 4, 5, 5, 7]

# These three methods all change the list without changing the 
# memory address

# Are there ways to make new lists with new memory addresses?
# Yes
list1 = ['september', 'october', 'november']
list1
['september', 'october', 'november']
list2 = list1 + ['december']
list2
['september', 'october', 'november', 'december']
list1
['september', 'october', 'november']
id(list1)
4522580680
id(list2)
4522578376
# different memory addresses

# make a full copy of a list at a different memory address:
list3 = list2[:]
list3
['september', 'october', 'november', 'december']
list2
['september', 'october', 'november', 'december']
list3.append('january')
list3
['september', 'october', 'november', 'december', 'january']
list2
['september', 'october', 'november', 'december']
id(list3)
4522870088
id(list2)
4522578376

# summary:
# operations that create new lists (with different memory addresses):
#  1. constructing a new list [.,.,..]
#  2. slicing [:], [1:2]
#  3. concatenation: list2 = list1 + [...]
# operations that modify/mutate an exisiting list (no new list or mem
# address):
#  1. list.append
#  2. list.insert
#  3. list.remove
#  4. list.sort
#  5. most other list methods (but not all)

empty_list = []
empty_list
[]
empty_list2 = []
id(empty_list)
4522580552
id(empty_list2)
4520617736
empty_list1.append('hello')
Traceback (most recent call last):
  Python Shell, prompt 82, line 1
builtins.NameError: name 'empty_list1' is not defined
empty_list.append('hello')
empty_list
['hello']
empty_list2
[]

# Strings are *not* mutable
s = 'time'
# how can we change s to refer to the string 'lime'?
# can we change one letter in s in place?
s[0] = 'l'
Traceback (most recent call last):
  Python Shell, prompt 90, line 1
builtins.TypeError: 'str' object does not support item assignment
# strings are not mutable
# we can index them s[0], but we cannot change the characters in place
# and have s change autoatically

# since lists are mutable, we can do this
l1
[1, 2, 3, 'cat']
l1[0] = 'hi'
l1
['hi', 2, 3, 'cat']
id(l1)
4522708488
l1[2] = 777
l1
['hi', 2, 777, 'cat']
id(l1)
4522708488

s
'time'
id(s)
4519967072
s = 'l' + s[1:]
s
'lime'
id(s)
4522538968
s[0] = 'l'
Traceback (most recent call last):
  Python Shell, prompt 107, line 1
builtins.TypeError: 'str' object does not support item assignment

# Do not forget: Strings are *not* mutable

help(range)
Help on class range in module builtins:

class range(object)
 |  range(stop) -> range object
 |  range(start, stop[, step]) -> range object
 |  
 |  Return an object that produces a sequence of integers from start (inclusive)
 |  to stop (exclusive) by step.  range(i, j) produces i, i+1, i+2, ..., j-1.
 |  start defaults to 0, and stop is omitted!  range(4) produces 0, 1, 2, 3.
 |  These are exactly the valid indices for a list of 4 elements.
 |  When step is given, it specifies the increment (or decrement).
 |  
 |  Methods defined here:
 |  
 |  __bool__(self, /)
 |      self != 0
 |  
 |  __contains__(self, key, /)
 |      Return key in self.
 |  
 |  __eq__(self, value, /)
 |      Return self==value.
 |  
 |  __ge__(self, value, /)
 |      Return self>=value.
 |  
 |  __getattribute__(self, name, /)
 |      Return getattr(self, name).
 |  
 |  __getitem__(self, key, /)
 |      Return self[key].
 |  
 |  __gt__(self, value, /)
 |      Return self>value.
 |  
 |  __hash__(self, /)
 |      Return hash(self).
 |  
 |  __iter__(self, /)
 |      Implement iter(self).
 |  
 |  __le__(self, value, /)
 |      Return self<=value.
 |  
 |  __len__(self, /)
 |      Return len(self).
 |  
 |  __lt__(self, value, /)
 |      Return self<value.
 |  
 |  __ne__(self, value, /)
 |      Return self!=value.
 |  
 |  __reduce__(...)
 |      Helper for pickle.
 |  
 |  __repr__(self, /)
 |      Return repr(self).
 |  
 |  __reversed__(...)
 |      Return a reverse iterator.
 |  
 |  count(...)
 |      rangeobject.count(value) -> integer -- return number of occurrences of value
 |  
 |  index(...)
 |      rangeobject.index(value, [start, [stop]]) -> integer -- return index of value.
 |      Raise ValueError if the value is not present.
 |  
 |  ----------------------------------------------------------------------
 |  Static methods defined here:
 |  
 |  __new__(*args, **kwargs) from builtins.type
 |      Create and return a new object.  See help(type) for accurate signature.
 |  
 |  ----------------------------------------------------------------------
 |  Data descriptors defined here:
 |  
 |  start
 |  
 |  step
 |  
 |  stop

range(0, 10)
range(0, 10)

for i in range(0, 10):
    print(i)

0
1
2
3
4
5
6
7
8
9
for i in range(10):
    print(i)

0
1
2
3
4
5
6
7
8
9
for i in range(5, 10):
    print(i)

5
6
7
8
9
for i in range(3, 10, 2):
    print(i)

3
5
7
9
L
[1, 2, 3, 4, 5, 5, 7]
len(L)
7
for i in range(len(L)):
    print(i)

0
1
2
3
4
5
6
for i in range(len(L)):
    print(L[i])

1
2
3
4
5
5
7
L
[1, 2, 3, 4, 5, 5, 7]

# Worksheet

a = [1, 0]
a = a + [8]
a
[1, 0, 8]

a = [1, 0]
id(a)
4522561736
a = a + [8]
id(a)
4522562120
a = [a[0], a[1], 8]
a
[1, 0, 8]
id(a)
4522564744

a.append(8)
id(a)
4522564744
a.insert(len(a), 8)
a
[1, 0, 8, 8, 8]
len(a)
5
id(a)
4522564744

# 2.
a = [1,0,8]
b = a.sort()

a == [1, 0, 8]
False
a
[0, 1, 8]
a == [0, 1, 8]
True
b == [1, 0, 8]
False
b == [0, 1, 8]
False
b

# b = a.sort() sets the value of a.sort() to b
# but a.sort() only changes a and returns nothing
# so b has the value None
# a.sort() has a return value of None, which gets assigned to b

a = [0, 1, 2]
b = a
b[2] = 100
a == [0, 1, 2] and b == [0, 1, 100]
False
a == [0, 1, 2]
False
b == [0, 1, 100]
True
id(b)
4522562312
id(a)
4522562312

for i range(1, 24, 2):
    print('na')

Traceback (most recent call last):
  Python Shell, prompt 158, line 1
Syntax Error: invalid syntax: <string>, line 1, pos 11
for i in range(1, 24, 2):
    print('na')

na
na
na
na
na
na
na
na
na
na
na
na