range in Python (1)

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*Memo:

• My post explains the shallow and deep copy of a range.
• My post explains a list (1).
• My post explains a tuple.
• My post explains a set and the set with copy.
• My post explains a frozenset (1).
• My post explains a dictionary (1).
• My post explains an iterator (1).
• My post explains a string.
• My post explains a bytes.
• My post explains a bytearray.
• My post explains enumerate().
• My post explains zip().

A range:

• is the ordered collection of zero or more numbers whose type is range:
  • Ordered means that the order of the numbers in a range is kept so it guarantees that the order is always the same unless someone or something changes it.
• can be huge because it's the special object which always uses low memory not to get MemoryError and it's not an iterator.
• is immutable(hashable) so it cannot be changed.
• can be iterated with a for statement.
• can be unpacked with an assignment and for statement, function and * but not with **.
• is False if it's empty.
• can be checked if a specific element is in the range with in keyword.
• can be checked if the range is referred to by two variables with is keyword.
• cannot be enlarged with * and a number.
• can be created by range().
• can be used with len() to get the length.
• can be read but cannot be changed by indexing or slicing.
• can be continuously used through multiple variables.
• can be shallow-copied (only by slicing) but cannot be deep-copied.

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A range can be huge so it doesn't get MemoryError.

---

range() can create a range between [start, stop) as shown below:

*Memo:

• The 1st argument is start or stop(Required-Type:int):
  • It's a start index(inclusive) or stop index(exclusive).
  • Don't use start= or stop=.
• The 2nd argument is stop(Optional-Type:int):
  • It's a stop index(exclusive).
  • Don't use stop=.
• The 3rd argument is step(Optional-Default:1-Type:int):
  • It's the interval of elements.
  • It cannot be 0.
  • Don't use step=.
• Only if one argument is set, the 1st argument is stop, creating the range between [0, stop).

# Empty range
v = range(0)
v = range(0, 0)
v = range(0, 0, 1)
v = range(5, 5)
v = range(5, 5, 1)
v = range(-10)
v = range(10, -10)
v = range(-10, 10, -3)
v = range(10, -10, 3)
# No error

v = range(5)
v = range(0, 5)
v = range(0, 5, 1)
v = range(-10, 10, 3)
v = range(10, -10, -3)
# No error

for x in range(5): pass
v1, v2, v3 = range(3)
v1, *v2, v3 = range(6)
for v1, v2, v3 in [range(3), range(3, 6)]: pass
for v1, *v2, v3 in [range(6), range(6, 12)]: pass
print(*range(4), *range(4, 6))
print([*range(4), *range(4, 6)])
# No error

v = range(0, 5, 0)
v = range(5) * 3
# Error

A range is the ordered collection of zero or more numbers whose type is range as shown below:

*Memo:

• A range can be unpacked with *.
• A range can be read by indexing:
  • Indexing can be done with one or more [index].

v = range(5)
v = range(0, 5)
v = range(0, 5, 1)

print(v)
# range(0, 5)

print(type(v))
# <class 'range'>

print(v.start, v.stop, v.step)
# 0 5 1

print(*v)
print(v[0], v[1], v[2], v[3], v[4])
print(v[-5], v[-4], v[-3], v[-2], v[-1])
# 0 1 2 3 4

v = range(0, 5, 0)
# ValueError: range() arg 3 must not be zero

# Empty range
v1 = range(0)
v2 = range(0, 0)
v3 = range(0, 0, 1)
v4 = range(5, 5)
v5 = range(5, 5, 1)

print(v1, v2, v3, v4, v5)
# range(0, 0) range(0, 0) range(0, 0) range(5, 5) range(5, 5)

print(v[0])
# IndexError: range object index out of range

v = range(-10, 10, 3)

print(v)
# range(-10, 10, 3)

print(*v)
print(v[0], v[1], v[2], v[3], v[4], v[5], v[6])
print(v[-7], v[-6], v[-5], v[-4], v[-3], v[-2], v[-1])
# -10 -7 -4 -1 2 5 8

v = range(10, -10, -3)

print(v)
# range(10, -10, -3)

print(*v)
print(v[0], v[1], v[2], v[3], v[4], v[5], v[6])
print(v[-7], v[-6], v[-5], v[-4], v[-3], v[-2], v[-1])
# 10 7 4 1 -2 -5 -8

v1 = range(-10)
v2 = range(10, -10)
v3 = range(-10, 10, -3)
v4 = range(10, -10, 3)

print(v1, v2, v3, v4)
# range(0, -10) range(10, -10) range(-10, 10, -3) range(10, -10, 3)

print(v1[0])
print(v2[0])
print(v3[0])
print(v4[0])
# IndexError: range object index out of range

A range can be read by slicing as shown below:

*Memo:

• Slicing can be done with one or more [start:end:step]:
  • start(Optional-Default:The index of the 1st element):
    • It's a start index(inclusive).
  • end(Optional-Default:The index of the last element + 1):
    • It's an end index(exclusive).
  • step(Optional-Default:1):
    • It's the interval of indices.
    • It cannot be zero.
  • The [] with at least one : is slicing.

v1 = range(10)

print(v1)
# range(0, 10)

print(*v1)
# 0 1 2 3 4 5 6 7 8 9

v2 = v1[2:8]
v2 = v1[-8:-2]

print(v2)
# range(2, 8)

print(*v2)
# 2 3 4 5 6 7

v2 = v1[2:8:2]
v2 = v1[-8:-2:2]

print(v2)
# range(2, 8)

print(*v2)
# 2 4 6

A range cannot be changed by indexing or slicing as shown below:

*Memo:

• A del statement can still be used to remove one or more variables themselves.

v = range(5)

v[0] = 10
v[2:5] = [20, 30]
# TypeError: 'range' object does not support item assignment

v = range(5)

del v[0], v[2:5]
# TypeError: 'range' object does not support item deletion

v = range(5)

del v

print(v)
# NameError: name 'v' is not defined

A range can be iterated with a for statement as shown below:

for x in range(5):
    print(x)
# 0
# 1
# 2
# 3
# 4

fruits = ["Apple", "Orange", "Banana", "Kiwi", "Lemon", "Mango"]

for i in range(4):
    print(fruits[i])
# Apple
# Orange
# Banana
# kiwi

for i in range(1, 6, 2):
    print(fruits[i])
# Orange
# Kiwi
# Mango

for i in range(5, 0, -2):
    print(fruits[i])
# Mango
# Kiwi
# Orange

A range can be unpacked with an assignment and for statement, function and * but not with ** as shown below:

v1, v2, v3 = range(3)

print(v1, v2, v3)
# 0 1 2

v1, *v2, v3 = range(6)

print(v1, v2, v3)  # 0 [1, 2, 3, 4] 5
print(v1, *v2, v3) # 0 1 2 3 4 5

for v1, v2, v3 in [range(3), range(3, 6)]:
    print(v1, v2, v3)
# 0 1 2
# 3 4 5

for v1, *v2, v3 in [range(6), range(6, 12)]:
    print(v1, v2, v3)
    print(v1, *v2, v3)
# 0 [1, 2, 3, 4] 5
# 0 1 2 3 4 5
# 6 [7, 8, 9, 10] 11
# 6 7 8 9 10 11

print(*range(4), *range(4, 6))
# 0 1 2 3 4 5

print([*range(4), *range(4, 6)])
# [0, 1, 2, 3, 4, 5]

def func(p1='a', p2='b', p3='c', p4='d', p5='e', p6='f'):
    print(p1, p2, p3, p4, p5, p6)

func()
# a b c d e f

func(*range(4), *range(4, 6))
# 0 1 2 3 4 5

def func(p1='a', p2='b', *args):
    print(p1, p2, args)
    print(p1, p2, *args)
    print(p1, p2, ['A', 'B', *args, 'C', 'D'])

func()
# a b ()
# a b Nothing
# a b ['A', 'B', 'C', 'D']

func(*range(4), *range(4, 6))
# 0 1 (2, 3, 4, 5)
# 0 1 2 3 4 5
# 0 1 ['A', 'B', 2, 3, 4, 5, 'C', 'D']

An empty range is False as shown below:

print(bool(range(0))) # Empty range
# False

A range can be checked if a specific element is in the range with in keyword as shown below:

v = range(4)

print(*v)
# 0 1 2 3

print(2 in v)
# True

print(4 in v)
# False

A range cannot be enlarged with * and a number as shown below:

v = range(5) * 3
# TypeError: unsupported operand type(s) for *: 'range' and 'int'

A range can be used with len() to get the length as shown below:

v = range(5)

print(*v)
# 0 1 2 3 4

print(len(v))
# 5

A range can be continuously used through multiple variables as shown below:

v1 = v2 = v3 = range(5) # Equivalent
                        # v1 = range(5)
                        # v2 = v1
                        # v3 = v2
print(v1, *v1) # range(0, 5) 0 1 2 3 4
print(v2, *v2) # range(0, 5) 0 1 2 3 4
print(v3, *v3) # range(0, 5) 0 1 2 3 4

A range can be shallow-copied (only by slicing) but cannot deep-copied as shown below:

<Shallow copy>:

*Memo:

• v1 and v2 refer to different ranges (only by slicing) and each same element.
• is keyword can check if v1 and v2 refer to the same range and/or each same element.
• Slicing can shallow-copy the range.
• copy.copy() cannot shallow-copy a range.

v1 = range(5)
v2 = v1[:]

print(v1, *v1) # range(0, 5) 0 1 2 3 4
print(v2, *v2) # range(0, 5) 0 1 2 3 4

print(v1 is v2, v1[2] is v2[2])
# False True

import copy

v1 = range(5)
v2 = copy.copy(v1)

print(v1, *v1) # range(0, 5) 0 1 2 3 4
print(v2, *v2) # range(0, 5) 0 1 2 3 4

print(v1 is v2, v1[2] is v2[2])
# True True

<Deep copy>:

*Memo:

• v1 and v2 refer to the same range and each same element.
• copy.deepcopy() cannot deep-copy and even shallow-copy a range.

import copy

v1 = range(5)
v2 = copy.deepcopy(v1)

print(v1, *v1) # range(0, 5) 0 1 2 3 4
print(v2, *v2) # range(0, 5) 0 1 2 3 4

print(v1 is v2, v1[2] is v2[2])
# True True

index() can get the index of the element matched to value from the range as shown below:

*Memo:

• The 1st argument is value(Required-Type:Any).
• Error occurs if value doesn't exist.

v = range(5, 10)

print(*v)
# 5 6 7 8 9

print(v.index(7)) # 2
print(v.index(10)) # ValueError: 10 is not in range

count() can count the elements matched to value in the range as shown below:

*Memo:

• The 1st argument is value(Required-Type:Any):
  • Don't use value=.

v = range(5, 10)

print(*v)
# 5 6 7 8 9

print(v.count(7))  # 1
print(v.count(10)) # 0

sorted() can convert a range to a list, then sort the list as shown below:

*Memo:

• The 1st argument is iterable(Required-Type:Iterable):
  • Don't use iterable=.
• The 2nd argument is key(Optional-Default:None-Type:Callable or NoneType).
• The 3rd argument is reverse(Optional-Default:False-Type:bool) to reverse the list.
• sorted() creates a copy:
  • Be careful, sorted() does shallow copy instead of deep copy as my issue.

v = range(-3, 3)

print(*v)
# -3 -2 -1 0 1 2

print(sorted(v))
print(sorted(v, key=None, reverse=False))
# [-3, -2, -1, 0, 1, 2]

print(sorted(v, reverse=True))
# [2, 1, 0, -1, -2, -3]

print(sorted(v, key=abs))
# [0, -1, 1, -2, 2, -3]

print(sorted(v, key=abs, reverse=True))
# [-3, -2, 2, -1, 1, 0]

reversed() can return the iterator which has the reversed elements of a range as shown below:

*Memo:

• The 1st argument is seq(Required-Type:Sequence):
  • Don't use seq=.

v = range(5)

print(*v)
# 0 1 2 3 4

print(reversed(v))
# <range_iterator object at 0x0000023D03BF5030>

print(*reversed(v))
# 4 3 2 1 0