More practice exersizes

KitN · KitN · commit 70df29d01419 · 2022-04-11T14:08:48.000+08:00
diff --git a/code/markovattempt.py b/code/markovattempt.py
@@ -0,0 +1,120 @@
+"""This module contains a code example related to
+
+Think Python, 2nd Edition
+by Allen Downey
+http://thinkpython2.com
+
+Copyright 2015 Allen Downey
+
+License: http://creativecommons.org/licenses/by/4.0/
+"""
+
+from __future__ import print_function, division
+
+import sys
+import string
+import random
+
+class Markov:
+    def __init__(self):
+        self.suffix_map = {}        # map from prefixes to a list of suffixes
+        self.prefix = ()            # current tuple of words
+
+    def process_file(self, filename, order=2):
+        """Reads a file and performs Markov analysis.
+
+        filename: string
+        order: integer number of words in the prefix
+
+        returns: map from prefix to list of possible suffixes.
+        """
+        fp = open(filename)
+        self.skip_gutenberg_header(fp)
+
+        for line in fp:
+            if line.startswith('*** END OF THIS'): 
+                break
+
+            for word in line.rstrip().split():
+                self.process_word(word, order)
+
+    def skip_gutenberg_header(self, fp):
+        """Reads from fp until it finds the line that ends the header.
+
+        fp: open file object
+        """
+        for line in fp:
+            if line.startswith('*** START OF THIS'):
+                break
+
+
+    def process_word(self, word, order=2):
+        """Processes each word.
+
+        word: string
+        order: integer
+
+        During the first few iterations, all we do is store up the words; 
+        after that we start adding entries to the dictionary.
+        """
+        if len(self.prefix) < order:
+            self.prefix += (word,)
+            return
+
+        try:
+            self.suffix_map[self.prefix].append(word)
+        except KeyError:
+            # if there is no entry for this prefix, make one
+            self.suffix_map[self.prefix] = [word]
+
+        self.prefix = self.shift(self.prefix, word)
+
+    def shift(self, t, word):
+        """Forms a new tuple by removing the head and adding word to the tail.
+
+        t: tuple of strings
+        word: string
+
+        Returns: tuple of strings
+        """
+        return t[1:] + (word,)
+
+    def random_text(self, n=100):
+        """Generates random wordsfrom the analyzed text.
+
+        Starts with a random prefix from the dictionary.
+
+        n: number of words to generate
+        """
+        # choose a random prefix (not weighted by frequency)
+        start = random.choice(list(self.suffix_map.keys()))
+        
+        for i in range(n):
+            suffixes = self.suffix_map.get(start, None)
+            if suffixes == None:
+                # if the start isn't in map, we got to the end of the
+                # original text, so we have to start again.
+                self.random_text(n-i)
+                return
+
+            # choose a random suffix
+            word = random.choice(suffixes)
+            print(word, end=' ')
+            start = self.shift(start, word)
+
+
+def main(script, filename='158-0.txt', n=100, order=2):
+    try:
+        n = int(n)
+        order = int(order)
+    except ValueError:
+        print('Usage: %d filename [# of words] [prefix length]' % script)
+    else: 
+        m = Markov()
+        m.process_file(filename, order)
+        m.random_text(n)
+        print()
+
+
+if __name__ == '__main__':
+    main(*sys.argv)
