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In [[Python]], '''sequence''' is the generic term for an ordered set.  There are several types of sequences in Python, the following three are the most important.

[[List]]s are the most versatile sequence type.  The elements of a list can be any object, and lists are '''mutable''' - they can be changed.  Elements can be reassigned or removed, and new elements can be inserted.

[[Tuple]]s are like lists, but they are '''immutable''' - they can't be changed.

[[String]]s are a special type of sequence that can only store [[character]]s, and they have a special notation.  However, all of the sequence operations described  below can also be used on strings.

==Sequence Operations==
*+ combines two sequences in a process called '''concatenation'''.  For example, <tt>[1,2,3]+[4,5]</tt> will evaluate to <tt>[1,2,3,4,5]</tt>.
*<nowiki>*</nowiki> repeats a sequence a (positive integral) number of times.  For example, <tt>[1,11]*3</tt> will evaluate to <tt>[1,11,1,11,1,11]</tt>.
*<tt>x '''in''' mySeq</tt> will return True if x is an element of mySeq, and False otherwise.  You can negate this statement with either <tt>not (x in mySeq)</tt> or <tt>x not in mySeq</tt>.
*<tt>mySeq[i]</tt> will return the i'th character of mySeq.  Sequences in Python are '''zero-indexed''', so the first element has index 0, the second has index 1, and so on.
*<tt>mySeq[-i]</tt> will return the i'th element from the end of mySeq, so <tt>mySeq[-1]</tt> is the last element of mySeq, <tt>mySeq[-2]</tt> is the second-to-last element, etc.
*All sequences can be [[slice]]d.

==Useful Functions==
*<tt>'''len'''(mySeq)</tt>, short for length, returns the number of elements in the sequence mySeq.
====Searching====
*<tt>mySeq.'''index'''(x)</tt> returns the index of the first occurrence of x in mySeq.  Note that if x isn't in mySeq index will return an error.
*<tt>mySeq.'''find'''(x)</tt> does the same thing as <tt>index</tt>, but returns -1 if x isn't an element, rather than throwing an error.
*<tt>'''min'''(mySeq)</tt> and <tt>'''max'''(mySeq)</tt> return the smallest and largest elements of mySeq, respectively.  If the elements are strings this would be the first and last elements in lexicographic order (the order of words in a dictionary).  Note that if any two elements in mySeq are incomparable (a string and a number, for example), min and max will return errors.
*<tt>mySeq.'''rindex'''(x)</tt> and <tt>mySeq.'''rfind'''(x)</tt> (short for right index and right find) return the ''last'' occurrence of x in mySeq.
*<tt>mySeq.'''count'''(x)</tt> returns the number of occurrences of x in mySeq (that is, the number of elements in mySeq that are equal to x).

==See Also==
[http://docs.python.org/py3k/library/stdtypes.html#sequence-types-str-bytes-bytearray-list-tuple-range Python 3.2 Documentation]

[[Category:Introduction to Programming]]