Added parsing for monzos and support for escaped pitch_classes

Syntax for monzos supported in scala scales: [-1 1> etc.

Support for escaped pitches: {q12 e23 26}

ziffers/generators.py

@@ -0,0 +1,35 @@
+"""Collection of generators"""
+
+
+# Sieve of Eratosthenes
+# Based on code by David Eppstein, UC Irvine, 28 Feb 2002
+# http://code.activestate.com/recipes/117119/
+def gen_primes():
+    """Generate an infinite sequence of prime numbers."""
+    # Maps composites to primes witnessing their compositeness.
+    # This is memory efficient, as the sieve is not "run forward"
+    # indefinitely, but only as long as required by the current
+    # number being tested.
+    sieve = {}
+
+    # The running integer that's checked for primeness
+    current = 2
+
+    while True:
+        if current not in sieve:
+            # current is a new prime.
+            # Yield it and mark its first multiple that isn't
+            # already marked in previous iterations
+            yield current
+            sieve[current * current] = [current]
+        else:
+            # current is composite. sieve[current] is the list of primes that
+            # divide it. Since we've reached current, we no longer
+            # need it in the map, but we'll mark the next
+            # multiples of its witnesses to prepare for larger
+            # numbers
+            for composite in sieve[current]:
+                sieve.setdefault(composite + current, []).append(composite)
+            del sieve[current]
+
+        current += 1