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POEM ID: 067
Title: Add a method to Vector to compute a hash.
authors: @naylor-b
Competing POEMs:
Related POEMs:
Associated implementation PR: #2534

Status:

  • Active
  • Requesting decision
  • Accepted
  • Rejected
  • Integrated

Motivation

There may be occasions when a developer may want to detect if a Vector has changed without having to keep a copy of the Vector around in order to be able to detect differences between the Vector's old and new versions. Computing a hash of the Vector would provide a simple way to accomplish this.

Proposed solutions

The following new method will be added to the Vector class.

def get_hash(self, alg=hashlib.sha1):
    """
    Return a hash string for the array contained in this Vector.

    Parameters
    ----------
    alg : function
        Algorithm used to generate the hash.  Default is hashlib.sha1.

    Returns
    -------
    str
        The hash string.
    """

Example

To compute a hash for our inputs vector for example:

self.oldhash = self._inputs.get_hash()

Then later, to detect if the inputs have changed:

newhash = self._inputs.get_hash()

if self.oldhash == newhash:  #  self._inputs have not changed
    # reuse cached solution
else:   # self._inputs have changed
    self.oldhash = newhash
    # recompute solution and save it to cache