<p dir="auto">related <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="16188429" data-permission-text="Title is private" data-url="https://github.com/pandas-dev/pandas/issues/4088" data-hovercard-type="issue" data-hovercard-url="/pandas-dev/pandas/issues/4088/hovercard" href="https://github.com/pandas-dev/pandas/issues/4088">#4088</a><br>
related <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="38981460" data-permission-text="Title is private" data-url="https://github.com/pandas-dev/pandas/issues/7867" data-hovercard-type="pull_request" data-hovercard-url="/pandas-dev/pandas/pull/7867/hovercard" href="https://github.com/pandas-dev/pandas/pull/7867">#7867</a></p>
<p dir="auto">I think this should raise as this is not clear how this should work (e.g. should you get all the other levels set to <code class="notranslate">nan</code>?)</p>
<p dir="auto">or see my comment below, maybe just document?</p>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="In [11]: s = pd.Series(np.arange(9),index=pd.MultiIndex.from_product([['A','B','C'],['foo','bar','baz']],names=['one','two'])).sortlevel()

In [12]: s
Out[12]: 
one  two
A    bar    1
     baz    2
     foo    0
B    bar    4
     baz    5
     foo    3
C    bar    7
     baz    8
     foo    6
dtype: int64

In [13]: s.reindex(['A','B','D'],level=0)
Out[13]: 
one  two
A    bar    1
     baz    2
     foo    0
B    bar    4
     baz    5
     foo    3
dtype: int64"><pre class="notranslate"><code class="notranslate">In [11]: s = pd.Series(np.arange(9),index=pd.MultiIndex.from_product([['A','B','C'],['foo','bar','baz']],names=['one','two'])).sortlevel()

In [12]: s
Out[12]: 
one  two
A    bar    1
     baz    2
     foo    0
B    bar    4
     baz    5
     foo    3
C    bar    7
     baz    8
     foo    6
dtype: int64

In [13]: s.reindex(['A','B','D'],level=0)
Out[13]: 
one  two
A    bar    1
     baz    2
     foo    0
B    bar    4
     baz    5
     foo    3
dtype: int64
</code></pre></div>
<p dir="auto">I'm moving this to an issue so it's easier to track and I can split into separate, smaller, pull requests. (previously was <a class="issue-link js-issue-link" data-error-text="Failed to load title" data-id="15608264" data-permission-text="Title is private" data-url="https://github.com/pandas-dev/pandas/issues/3924" data-hovercard-type="pull_request" data-hovercard-url="/pandas-dev/pandas/pull/3924/hovercard" href="https://github.com/pandas-dev/pandas/pull/3924">#3924</a>).</p>
<p dir="auto">For right now, the goal is to take care of the low-hanging fruit (the really obvious items that should be TypeError, ValueError, etc.) and then potentially take on more of the code base later.</p>
<p dir="auto">Packages/Files where exceptions have been changed (will be checked off once test cases are edited for them)</p>
<ul class="contains-task-list">
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> <code class="notranslate">merge</code></li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> <code class="notranslate">stats/common</code></li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> <code class="notranslate">tools/tile</code></li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> <code class="notranslate">core/common</code></li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> <code class="notranslate">core/format</code></li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> <code class="notranslate">core/frame</code></li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> <code class="notranslate">pandas/sparse</code></li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> <code class="notranslate">pandas/tseries</code></li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox"> <code class="notranslate">core/internals</code></li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> <code class="notranslate">core/index</code></li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox"> <code class="notranslate">core/panel</code></li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox"> <code class="notranslate">core/series</code></li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox"> <code class="notranslate">core/panelnd</code></li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox"> <code class="notranslate">rpy/common</code></li>
<li class="task-list-item"><input type="checkbox" id="" disabled="" class="task-list-item-checkbox" checked=""> <code class="notranslate">io/excel</code></li>
</ul>
<p dir="auto">More to come...</p>