Implemented smart autoindenting.

IPython/frontend/html/notebook/static/css/notebook.css

@@ -83,6 +83,10 b' span.section_row_buttons > button {'
     float: right;
 }
 
+#autoindent_span {
+    float: right;
+}
+
 .checkbox_label {
     font-size: 85%;
     float: right;

IPython/frontend/html/notebook/static/js/cell.js

@@ -68,6 +68,17 b' var IPython = (function (IPython) {'
     };
 
 
+    Cell.prototype.set_autoindent = function (state) {
+        if (state) {
+            this.code_mirror.setOption('tabMode', 'indent');
+            this.code_mirror.setOption('enterMode', 'indent');
+        } else {
+            this.code_mirror.setOption('tabMode', 'shift');
+            this.code_mirror.setOption('enterMode', 'flat');
+        }
+    };
+
+
     // Subclasses must implement create_element.
     Cell.prototype.create_element = function () {};
 

IPython/frontend/html/notebook/static/js/codecell.js

@@ -48,8 +48,7 b' var IPython = (function (IPython) {'
         if (event.keyCode === 13 && event.shiftKey) {
             // Always ignore shift-enter in CodeMirror as we handle it.
             return true;
-        // } else if (event.keyCode == 32 && (event.ctrlKey || event.metaKey) && !event.altKey) {
-        } else if (event.keyCode == 9) {
+        } else if (event.keyCode === 9) {
             var cur = editor.getCursor();
             var pre_cursor = editor.getRange({line:cur.line,ch:0},cur).trim();
             if (pre_cursor === "") {
@@ -65,6 +64,21 b' var IPython = (function (IPython) {'
                 IPython.notebook.complete_cell(this, line, cur.ch);
                 return true;
             }
+        } else if (event.keyCode === 8) {
+            // If backspace and the line ends with 4 spaces, remove them.
+            var cur = editor.getCursor();
+            var line = editor.getLine(cur.line);
+            var ending = line.slice(-4);
+            if (ending === '    ') {
+                editor.replaceRange('',
+                    {line: cur.line, ch: cur.ch-4},
+                    {line: cur.line, ch: cur.ch}
+                );
+                event.stop();
+                return true;
+            } else {
+                return false;
+            };
         } else {
             if (this.is_completing && this.completion_cursor !== editor.getCursor()) {
                 this.is_completing = false;

IPython/frontend/html/notebook/static/js/notebook.js

@@ -447,6 +447,14 b' var IPython = (function (IPython) {'
     };
 
 
+    Notebook.prototype.set_autoindent = function (state) {
+        var cells = this.cells();
+        len = cells.length;
+        for (var i=0; i<len; i++) {
+            cells[i].set_autoindent(state)
+        };
+    };
+
     // Kernel related things
 
     Notebook.prototype.start_kernel = function () {

IPython/frontend/html/notebook/static/js/panelsection.js

@@ -167,6 +167,10 b' var IPython = (function (IPython) {'
         this.content.find('#run_all_cells').click(function () {
             IPython.notebook.execute_all_cells();
         });
+        this.content.find('#autoindent').change(function () {
+            var state = $('#autoindent').prop('checked');
+            IPython.notebook.set_autoindent(state);
+        });
     };
 
 

IPython/frontend/html/notebook/templates/notebook.html

@@ -119,6 +119,12 b''
                     </span>
                     <span class="button_label">Run</span>
                 </div>
+                <div class="section_row">
+                    <span id="autoindent_span">
+                        <input type="checkbox" id="autoindent"></input>
+                    </span>
+                    <span class="checkbox_label">Autoindent:</span>
+                </div>
             </div>
         </div>