Python implementation for psource (aimacode#613) (aimacode#619)

* Added python code for psource (aimacode#613)

* added psource code with optional highlighting (aimacode#613)

notebook.py

@@ -1,3 +1,5 @@
+from inspect import getsource
+
 from utils import argmax, argmin
 from games import TicTacToe, alphabeta_player, random_player, Fig52Extended, infinity
 from logic import parse_definite_clause, standardize_variables, unify, subst
@@ -24,6 +26,23 @@ def psource(*functions):
 # ______________________________________________________________________________
 
 
+def psource(*functions):
+    "Print the source code for the given function(s)."
+    source_code = '\n\n'.join(getsource(fn) for fn in functions)
+    try:
+        from pygments.formatters import HtmlFormatter
+        from pygments.lexers import PythonLexer
+        from pygments import highlight
+
+        display(HTML(highlight(source_code, PythonLexer(), HtmlFormatter(full=True))))
+
+    except ImportError:
+        print(source_code)
+
+
+# ______________________________________________________________________________
+
+
 def show_iris(i=0, j=1, k=2):
     """Plots the iris dataset in a 3D plot.
     The three axes are given by i, j and k,