Be more explicit about replace examples

Author: jerry-git

notebooks/beginner/html/strings.html

@@ -12015,13 +12015,22 @@ <h2 id="str.replace()"><code>str.replace()</code><a class="anchor-link" href="#s
 </div>
 </div>
 
+</div>
+<div class="cell border-box-sizing text_cell rendered"><div class="prompt input_prompt">
+</div>
+<div class="inner_cell">
+<div class="text_cell_render border-box-sizing rendered_html">
+<p>This will not modify <code>my_string</code> because replace is not done in-place.</p>
+
+</div>
+</div>
 </div>
 <div class="cell border-box-sizing code_cell rendered">
 <div class="input">
 <div class="prompt input_prompt">In&nbsp;[7]:</div>
 <div class="inner_cell">
  <div class="input_area">
-<div class=" highlight hl-ipython3"><pre><span></span><span class="n">my_string</span> <span class="o">=</span> <span class="n">my_string</span><span class="o">.</span><span class="n">replace</span><span class="p">(</span><span class="s1">&#39;a&#39;</span><span class="p">,</span> <span class="s1">&#39;?&#39;</span><span class="p">)</span>
+<div class=" highlight hl-ipython3"><pre><span></span><span class="n">my_string</span><span class="o">.</span><span class="n">replace</span><span class="p">(</span><span class="s1">&#39;a&#39;</span><span class="p">,</span> <span class="s1">&#39;?&#39;</span><span class="p">)</span>
 <span class="nb">print</span><span class="p">(</span><span class="n">my_string</span><span class="p">)</span>
 </pre></div>
 
@@ -12039,14 +12048,23 @@ <h2 id="str.replace()"><code>str.replace()</code><a class="anchor-link" href="#s
 
 
 <div class="output_subarea output_stream output_stdout output_text">
-<pre>Python is my f?vorite progr?mming l?ngu?ge!
+<pre>Python is my favorite programming language!
 </pre>
 </div>
 </div>
 
 </div>
 </div>
 
+</div>
+<div class="cell border-box-sizing text_cell rendered"><div class="prompt input_prompt">
+</div>
+<div class="inner_cell">
+<div class="text_cell_render border-box-sizing rendered_html">
+<p>You have to store the return value of <code>replace</code> instead.</p>
+
+</div>
+</div>
 </div>
 <div class="cell border-box-sizing code_cell rendered">
 <div class="input">
@@ -12071,7 +12089,7 @@ <h2 id="str.replace()"><code>str.replace()</code><a class="anchor-link" href="#s
 
 
 <div class="output_subarea output_stream output_stdout output_text">
-<pre>Python will be my f?vorite progr?mming l?ngu?ge!
+<pre>Python will be my favorite programming language!
 </pre>
 </div>
 </div>

notebooks/beginner/strings.ipynb

@@ -86,16 +86,30 @@
  "help(str.replace)"
  ]
  },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "This will not modify `my_string` because replace is not done in-place."
+ ]
+ },
  {
  "cell_type": "code",
  "execution_count": null,
  "metadata": {},
  "outputs": [],
  "source": [
- "my_string = my_string.replace('a', '?')\n",
+ "my_string.replace('a', '?')\n",
  "print(my_string)"
  ]
  },
+ {
+ "cell_type": "markdown",
+ "metadata": {},
+ "source": [
+ "You have to store the return value of `replace` instead."
+ ]
+ },
  {
  "cell_type": "code",
  "execution_count": null,