Copy relevant source code samples

Author: gjbex

source-code/cmd/README.md

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+# Cmd
+Standard Python library framework to facilitate writing command line
+driven interpreters.
+
+## What is it?
+1. `simple.py`: a very simmple example that keeps track of a list of
+    friends.  A friend is added by saying `hi` to her, and is removed by
+    saying `bye` to her.  You can't say `hi` to someone who is your friend
+    already, and you can't say `bye` to someone who isn't your friend.
+    `show_friends` lists the current friends.  `quit` exits the
+    application.  Note that `help` and tab completion are automatically
+    provided.

source-code/cmd/simple.py

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+#!/usr/bin/env python
+
+import cmd
+
+
+class HelloShell(cmd.Cmd):
+    intro = 'Welcome to the HelloShell, type ? to see a list of commands'
+    prompt = 'hello> '
+
+    def __init__(self):
+        '''constructor'''
+        super().__init__()
+        self._people = set()
+
+    def do_hi(self, args):
+        '''say hi'''
+        if args in self._people:
+            print('already said hi to {0}'.format(args))
+        else:
+            self._people.add(args)
+            print('hi {0}'.format(args))
+
+    def do_bye(self, args):
+        '''say bye'''
+        if args in self._people:
+            self._people.remove(args)
+            print('bye {0}'.format(args))
+        else:
+            print('never said hi to {0}'.format(args))
+
+    def do_show_friends(self, args):
+        '''show all current friends'''
+        if self._people:
+            print('all friends: {0}'.format(', '.join(self._people)))
+        else:
+            print('lonely, no friends')
+
+    def do_quit(self, args):
+        '''quit the HelloShell'''
+        print('thanks for coming by')
+        return True
+
+if __name__ == '__main__':
+    HelloShell().cmdloop()

source-code/code-evaluation/README.md

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+EvaluateCode
+============
+
+Python allows executino of Python source code at runtime.  Although this
+is a powerful feature, it should be used with extreme care, since it can
+give rise to serious security issues.
+
+What is it?
+-----------
+1. `evaluate.py`: short example that reads a code fragment, evaluates it,
+    and prints all values of variables defined in that code fragment.
+    Only variables of type `int`, '`float`, `str`, `bool` and `list` will
+    be printed.`
+1. `source.py`: sample code to evaluate using `evaluate.py`.
+1. `nasty.py`: sample code to illustrate that `exec` can be harmful; will
+   delete `my_precious.txt`, which should be copied from `my_precious.orig`;
+   to be evaluated by `evaluate.py`.
+1. `my_precious.orig`: file to copy to `my_precious.txt`.
+1. `fib.py`: definition of Fibonacci function.
+1. `fac.py`: definition of the recursive permutation function.
+1. `fac_iter.py`: definition of the iterative permutation function.
+1. `exec.py`: script that illustrates various uses of `exec`.

source-code/code-evaluation/evaluate.py

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+#!/usr/bin/env python
+
+if __name__ == '__main__':
+    from argparse import ArgumentParser
+    arg_parser = ArgumentParser(description='Read and exectue Ptyhon '
+                                            'source code in a local '
+                                            'environment')
+    arg_parser.add_argument('file', help='Python file to parse')
+    options = arg_parser.parse_args()
+    with open(options.file, 'r') as source_file:
+        source = ''.join(source_file.readlines())
+    globals = {}
+    locals = {}
+    exec(source, globals, locals)
+    for obj, val in locals.items():
+        if type(val) in [int, float, str, bool]:
+            print('{0} = {1}'.format(obj, str(val)))

source-code/code-evaluation/exec.py

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+#!/usr/bin/env python
+
+# place definition in global scope
+with open('fib.py', 'r') as func_file:
+    func_str = ''.join(func_file.readlines())
+exec(func_str)
+n = 5
+print('fib({0:d}) = {1:d}'.format(n, fib(n)))
+
+# place definitions in private scope, no problem for non-recursive functions
+with open('fac_iter.py', 'r') as func_file:
+    func_str = ''.join(func_file.readlines())
+priv_globals = {}
+priv_locals = {}
+exec(func_str, priv_globals, priv_locals)
+print('fac({0:d}) = {1:d}'.format(n, priv_locals['fac_iter'](n)))
+
+# place definitions in private scope, problem for recursive functions
+with open('fac.py', 'r') as func_file:
+    func_str = ''.join(func_file.readlines())
+priv_globals = {}
+priv_locals = {}
+exec(func_str, priv_globals, priv_locals)
+try:
+    result = eval('fac({0})'.format(n), priv_globals, priv_locals)
+    print('fac({0:d}) = {1:d}'.format(n, result))
+except NameError as error:
+    print('Exception: {0}'.format(str(error)))
+
+# when evaluating within string, no problem
+exec('{0}\nresult = fac({1:d})'.format(func_str, 5))
+print('fac({0:d}) = {1:d}'.format(n, result))

source-code/code-evaluation/fac.py

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+def fac(n):
+    if n < 2:
+        return 1
+    else:
+        return n*fac(n-1)

source-code/code-evaluation/fac_iter.py

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+def fac_iter(n):
+    result = 1
+    for i in range(2, n + 1):
+        result *= i
+    return result

source-code/code-evaluation/fib.py

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+def fib(n):
+    if n == 0 or n == 1:
+        return 1
+    else:
+        return fib(n-1) + fib(n-2)

source-code/code-evaluation/my_precious.orig

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+This is very precious data.

source-code/code-evaluation/nasty.py

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+from pathlib import Path
+
+path = Path.cwd()
+path /= 'my_precious.txt'
+print('Now deleting your precious data...')
+path.unlink()