updated primes solution

Author: PythonCHB

source/class_schedule/session_2_01.rst

@@ -1,26 +1,40 @@
-#########################################
-Advanced Programming in Python: Session 1
-#########################################
+##############################################
+Session 1: Iterators and Generators, Packaging
+##############################################
 
-lambda
 
-closures
+* Iterators and iterables
 
+* The iteration protocol
 
-Pre-class prep
-==============
+* Iterable classes
 
-:ref:`anonymous_functions`
+* Generators
 
-:ref:`closures`
+* Packages and packaging
 
+Reading
+=======
+
+:ref:`iterators_generators`
+
+:ref:`packaging`
 
 Supplemental Readings
 =====================
 
-http://www.blog.pythonlibrary.org/2015/10/28/python-101-lambda-basics/
+Iterators and Generators
+........................
+
+*Fluent Python:* Chapter 14: Iterables, Iterators, and Generators
+
+Packages and Packaging
+......................
+
+https://packaging.python.org/
+
+http://pythonchb.github.io/PythonTopics/where_to_put_your_code.html
 
-https://pythonconquerstheuniverse.wordpress.com/2011/08/29/lambda_tutorial/
 
 Functools
 .........

source/modules/Packaging.rst

@@ -147,6 +147,8 @@ But ``distutils``  is missing some key features:
 
 Now it's pretty stable: pip+setuptools+wheel: use them.
 
+**warning** -- setuptools still provides easy_install, but it hss mostly been deprecated, so you really want to use pip. And sometimes setuptools will invoke it for you under the hood by accident :-(
+
 
 Installing Packages
 -------------------
@@ -159,21 +161,25 @@ But getting better, and the mess is *almost* cleaned up.
 Current State of Packaging
 --------------------------
 
-To build packages: distutils
+To build packages: setuptools
+.............................
+
+  * https://pythonhosted.org/setuptools/
 
-  * http://docs.python.org/3/distutils/
+setuptools provides extensions to the build-in distutils:
 
-For more features: setuptools
+https://docs.python.org/3/library/distutils.html
 
-  * https://pythonhosted.org/setuptools/
+But there are a couple of those extensions that you really do need, so most folks use setuptools for everything. In fact, pip itself requires setuptools.
 
-(note that setuptools still can also install -- but don't let it)
 
 To install packages: pip
+........................
 
   * https://pip.pypa.io/en/latest/installing.html
 
 For binary packages: wheels
+...........................
 
   * http://www.python.org/dev/peps/pep-0427/
 

source/solutions/iterators_generators/generators.py

@@ -55,3 +55,39 @@ def prime():  # 2, 3, 5, 7, 11, 13, 17, 19, 23...
                 if a % x == 0:
                     p = False           # ...unless it isn't
                     break
+
+def prime():  # 2, 3, 5, 7, 11, 13, 17, 19, 23...
+    """ note that this is NOT a very efficient way to compute primes!"""
+    n = 0
+    a = 2
+    while True:
+        yield a
+        p = False
+        while not p:   # while not prime
+            a += 1     # try the next integer
+            p = True   # assume it is prime...
+            for x in range(2, int(math.floor(math.sqrt(a))) + 1):
+                if a % x == 0:
+                    p = False           # ...unless it isn't
+                    break
+
+def prime2():  # 2, 3, 5, 7, 11, 13, 17, 19, 23...
+    """ This is a bit more efficient"""
+    # keep a list of the primes already generated
+    primes = []
+    a = 2
+    while True:
+        # print("adding %s to the list"%a)
+        primes.append(a)
+        yield a
+        p = False
+        while not p:   # while not prime
+            # try the next non-even integer
+            a += (2 if (a % 2) else 1)
+            p = True   # assume it is prime...
+            # test if it is divisible by any of the smaller primes
+            for x in primes:
+                if a % x == 0:
+                    p = False           # ...unless it isn't
+                    break
+

source/solutions/iterators_generators/sum67.py

@@ -3,7 +3,7 @@
 
 A student wondered if this exercise could be done with a generator.
 
-Indeed is can
+Indeed it can
 
 Return the sum of the numbers in the array, except ignore sections of
 numbers starting with a 6 and extending to the next 7 (every 6 will be

source/solutions/iterators_generators/test_generators.py

@@ -37,3 +37,15 @@ def test_prime():
     g = gs.prime()
     for val in [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]:
         assert next(g) == val
+
+
+def test_prime2():
+    """ same test as above, but a better algorithm """
+    g = gs.prime2()
+    for val in [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]:
+        p = next(g)
+        print("p is:", p)
+        assert p == val
+#    assert False
+
+