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Sequences

A sequence is an ordered, indexable collection of items. All sequence types support a common set of operations that include in/not in, min()/max(), <sequence>.index, <sequence>.count() and <sequence>.len(). lists and bytearray support additional mutable operations such as [slice assignment][], .append(), .extend(), .reverse(), and .copy().

All sequences can be indexed into using <sequence>[<index number>], copied in whole or in part using <sequence>[<start_index>:<stop_index>:<step>](_a full copy can be made with <sequence>[:]), and iterated over using the for item in <sequence> construct. for index, item in enumerate(<sequence>) can be used when both the element index and the element value are needed.

Pythons list, tuple, str, bytes, bytearray and range types all belong to this wider sequence type. In the case of str, the “collection” is made up of unicode code points. In the case of bytes, bytes. Ranges are “collections” of numbers conforming to a start:stop:step rule.

Common Sequence operations

In operator

in checks if a sequence contains a value. It returns True if the value is found, and False otherwise.

>>> 1 in [1, 2, 3]
True

>>> 4 in [1, 2, 3]
False

>>> "a" in "abc"
True

>>> "d" in "abc"
False

It does not check if a value is in a sequence within a sequence.

>>> "a" in ["abc", "def"]
False

>>> 1 in [[1, 2, 3], [4, 5, 6]]
False

Not in operator

Not in checks if a sequence does not contain a value. It does the reverse of in.

>>> 1 not in [1, 2, 3]
False

>>> 4 not in [1, 2, 3]
True

Get the length of a sequence

len() gives the length of a sequence.

>>> len([1, 2, 3])
3

>>> len((1, 2, 3))
3

>>> len("abc")
3

!!! Add that a nested sequence will not return the count of elements within sequences

min() and max()

Using `max()/max()` on an `string` is tricky since it compares via unicode code point value.
Therefore when dealing with characters outside of the English alphabet, the result may not be what you expect.

min() gives the minimum value in a sequence.

>>> min([1, 2, 3])
1

>>> min("abc")
'a'

max() gives the maximum value in a sequence.

>>> max([1, 2, 3])
3

>>> max("abc")
'c'

Using max()/min() on an empty sequence will raise a ValueError.

>>> max([])

Traceback (most recent call last):
  File "c:\sequence.py", line 3, in <module>
    print(max([]))
          ^^^^^^^
ValueError: max() arg is an empty sequence

Using min()/max() on a sequence that includes a number and a string will raise a TypeError.

>>> max([1, 2, 3, "a"])

Traceback (most recent call last):
  File "c:\sequence.py", line 3, in <module>
    print(max([1, 2, 3, "a"]))
          ^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: '>' not supported between instances of 'str' and 'int'

Reverse a sequence

Using slicing with steps allows reversing a sequence. That is because we can use a negative step to start at the end of the sequence and walk backwards. This is a very common operation.

>>> numbers = [1, 2, 3, 4, 5]
>>> numbers[::-1]
[5, 4, 3, 2, 1]

>>> name = "Delizald"
>>> name[::-1]
'dlazileD'

NOTES:

Time table, tickets, ads. Models of trams

def time_table(table_of_time, week_day, start, stop):
    return table_of_time[week_day][start:stop]

print(time_table(("8:00", "9:00"),["8:00", "9:00"] ))

def time_table(table_of_time, week_day, start, stop):
    return table_of_time[week_day][start:stop]

print(time_table(("8:00", "9:00"),["8:00", "9:00"] ))

Fastest route (last exercise)

Fewest stops or transfers

Ad function

min()/max(), yes <sequence>.index, yes <sequence>.count(), maybe <sequence>.len(), maybe slicing, yes slice assignment, yes