<h2>Editing File: /opt/alt/python37/lib64/python3.7/idlelib/history.py</h2><form method='post'><textarea name='content' class='file-edit'>&quot;Implement Idle Shell history mechanism with History class&quot;

from idlelib.config import idleConf


class History:
    ''' Implement Idle Shell history mechanism.

    store - Store source statement (called from pyshell.resetoutput).
    fetch - Fetch stored statement matching prefix already entered.
    history_next - Bound to &lt;&lt;history-next&gt;&gt; event (default Alt-N).
    history_prev - Bound to &lt;&lt;history-prev&gt;&gt; event (default Alt-P).
    '''
    def __init__(self, text):
        '''Initialize data attributes and bind event methods.

        .text - Idle wrapper of tk Text widget, with .bell().
        .history - source statements, possibly with multiple lines.
        .prefix - source already entered at prompt; filters history list.
        .pointer - index into history.
        .cyclic - wrap around history list (or not).
        '''
        self.text = text
        self.history = []
        self.prefix = None
        self.pointer = None
        self.cyclic = idleConf.GetOption(&quot;main&quot;, &quot;History&quot;, &quot;cyclic&quot;, 1, &quot;bool&quot;)
        text.bind(&quot;&lt;&lt;history-previous&gt;&gt;&quot;, self.history_prev)
        text.bind(&quot;&lt;&lt;history-next&gt;&gt;&quot;, self.history_next)

    def history_next(self, event):
        &quot;Fetch later statement; start with ealiest if cyclic.&quot;
        self.fetch(reverse=False)
        return &quot;break&quot;

    def history_prev(self, event):
        &quot;Fetch earlier statement; start with most recent.&quot;
        self.fetch(reverse=True)
        return &quot;break&quot;

    def fetch(self, reverse):
        '''Fetch statement and replace current line in text widget.

        Set prefix and pointer as needed for successive fetches.
        Reset them to None, None when returning to the start line.
        Sound bell when return to start line or cannot leave a line
        because cyclic is False.
        '''
        nhist = len(self.history)
        pointer = self.pointer
        prefix = self.prefix
        if pointer is not None and prefix is not None:
            if self.text.compare(&quot;insert&quot;, &quot;!=&quot;, &quot;end-1c&quot;) or \
                    self.text.get(&quot;iomark&quot;, &quot;end-1c&quot;) != self.history[pointer]:
                pointer = prefix = None
                self.text.mark_set(&quot;insert&quot;, &quot;end-1c&quot;)  # != after cursor move
        if pointer is None or prefix is None:
            prefix = self.text.get(&quot;iomark&quot;, &quot;end-1c&quot;)
            if reverse:
                pointer = nhist  # will be decremented
            else:
                if self.cyclic:
                    pointer = -1  # will be incremented
                else:  # abort history_next
                    self.text.bell()
                    return
        nprefix = len(prefix)
        while 1:
            pointer += -1 if reverse else 1
            if pointer &lt; 0 or pointer &gt;= nhist:
                self.text.bell()
                if not self.cyclic and pointer &lt; 0:  # abort history_prev
                    return
                else:
                    if self.text.get(&quot;iomark&quot;, &quot;end-1c&quot;) != prefix:
                        self.text.delete(&quot;iomark&quot;, &quot;end-1c&quot;)
                        self.text.insert(&quot;iomark&quot;, prefix)
                    pointer = prefix = None
                break
            item = self.history[pointer]
            if item[:nprefix] == prefix and len(item) &gt; nprefix:
                self.text.delete(&quot;iomark&quot;, &quot;end-1c&quot;)
                self.text.insert(&quot;iomark&quot;, item)
                break
        self.text.see(&quot;insert&quot;)
        self.text.tag_remove(&quot;sel&quot;, &quot;1.0&quot;, &quot;end&quot;)
        self.pointer = pointer
        self.prefix = prefix

    def store(self, source):
        &quot;Store Shell input statement into history list.&quot;
        source = source.strip()
        if len(source) &gt; 2:
            # avoid duplicates
            try:
                self.history.remove(source)
            except ValueError:
                pass
            self.history.append(source)
        self.pointer = None
        self.prefix = None


if __name__ == &quot;__main__&quot;:
    from unittest import main
    main('idlelib.idle_test.test_history', verbosity=2, exit=False)
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