Error installing ipdb for Python 2.7 using virtualenv and pip

When I tried to install ipdb, I had the following problem:

$ pip install ipdb
Collecting ipdb
  Using cached ipdb-0.10.3.tar.gz
    Complete output from command python setup.py egg_info:
    error in ipdb setup command: Invalid environment marker: python_version >= "3.3"

How can I install ipdb in the simplest way?

(I use macOS Sierra 10.12.4, virtualenv 1.11.6, python 2.7.10, pip 9.0.1)