Pip: Error in isso setup command: Invalid environment marker: python_version>="3.0"

[gntech]

When I try to install isso using pip on CentOS 7 I get the following error:

$ pip install isso
Downloading/unpacking isso
Downloading isso-0.10.1.tar.gz (95kB): 95kB downloaded
Running setup.py egg_info for package isso
error in isso setup command: Invalid environment marker: python_version>="3.0"
Complete output from command python setup.py egg_info:
error in isso setup command: Invalid environment marker: python_version>="3.0"

---

Cleaning up...
Command python setup.py egg_info failed with error code 1 in /home/gustav/isso/build/isso

[gntech]

It looks like it is asking for Python 3, but I am using Python 2.7.5
(Python 3 is not available on CentOS by default)

[gntech]

Upgrading pip solves the issue:

pip install --upgrade pip