iter(x) will raise a TypeError if x cannot be iterated on — but that check “accepts” sets and dictionaries, though it “rejects” other non-sequences such as None and numbers. On the other hands, strings (which most applications want to consider “single items” rather than sequences) are in fact sequences (so, any test, unless specialcased for … Read more
You can calculate values of sequences with a linear recurrence relation in O(log n) steps using the matrix method. In this case, the recurrence matrix is 2 2 1 0 The n-th term of the sequence is then obtained by multiplying the n-th power of that matrix with the two initial values. The recurrence immediately … Read more
OK, this is a very old question, which I’m first seeing now. You’ll need to differentiate between sequence numbers and unique IDs that are (optionally) loosely sortable by a specific criteria (typically generation time). True sequence numbers imply knowledge of what all other workers have done, and as such require shared state. There is no … Read more
As of 2.6, use abstract base classes. >>> import collections >>> isinstance([], collections.Sequence) True >>> isinstance(0, collections.Sequence) False Furthermore ABC’s can be customized to account for exceptions, such as not considering strings to be sequences. Here an example: import abc import collections class Atomic(object): __metaclass__ = abc.ABCMeta @classmethod def __subclasshook__(cls, other): return not issubclass(other, collections.Sequence) … Read more
You can create and use oracle sequences. The syntax and details are at http://www.techonthenet.com/oracle/sequences.php Also read the article http://rnyb2.blogspot.com/2006/02/potential-pitfall-with-oracle-sequence.html to understand the limitations with respect to AUTONUMBER in other RDBMS
All values in Python are references. What you need to worry about is if a type is mutable. The basic numeric and string types, as well as tuple and frozenset are immutable; names that are bound to an object of one of those types can only be rebound, not mutated. >>> t = 1, 2, … Read more
Sql Server 2012 has introduced SEQUENCE objects, which allow you to generate sequential numeric values not associated with any table. Creating them are easy: CREATE SEQUENCE Schema.SequenceName AS int INCREMENT BY 1 ; An example of using them before insertion: DECLARE @NextID int ; SET @NextID = NEXT VALUE FOR Schema.SequenceName; — Some work happens … Read more
The following is a simple example with a FOR UPDATE intention lock. A row-level lock with the INNODB engine. The sample shows four rows for next available sequences that will not suffer from the well-known INNODB Gap Anomaly (the case where gaps occur after failed usage of an AUTO_INCREMENT). Schema: — drop table if exists … Read more
With a comprehension? Well… >>> seq = ‘012345’ >>> swapped_pairs = zip(seq[1::2], seq[::2]) >>> ”.join(item for pair in swapped_pairs for item in pair) ‘103254’
Warning: boost::zip_iterator and boost::combine as of Boost 1.63.0 (2016 Dec 26) will cause undefined behavior if the length of the input containers are not the same (it may crash or iterate beyond the end). Starting from Boost 1.56.0 (2014 Aug 7) you could use boost::combine (the function exists in earlier versions but undocumented): #include <boost/range/combine.hpp> … Read more