Docker issue: /bin/sh: pip: not found : <p>So my dockerfile is :</p>

<pre><code>FROM iron/python:2.7

WORKDIR /app
ADD . /app

RUN pip install --upgrade pip
RUN pip install -r ./requirements.txt
</code></pre>

<p>Recently though when I build my image with:
    <code>docker build --no-cache -t &lt;image name&gt;:&lt;tag&gt;</code></p>

<p>I run into the issue of:</p>

<pre><code>Step 4/6 : RUN pip install --upgrade pip
---&gt; Running in 00c781a53487
/bin/sh: pip: not found
The command '/bin/sh -c pip install --upgrade pip' returned a non-zero code: 127
</code></pre>

<p>was there any changes to docker that might have caused this? Because last week this was all fine and there were no issues building the image with the same exact code. </p>
