A Comprehensive Guide to Resolving 'ImportError: No module named \'glob\'' in Python

Problem Background and Error Analysis

When running ROS Simulator on Ubuntu 14.04, the user encountered a common Python import error: ImportError: No module named 'glob'. This error indicates that the Python interpreter cannot find a module named glob in the current module search path. The user attempted to install the glob2 package, but the problem persisted, suggesting deeper issues with version compatibility or environment configuration.

Python Module Search Path Analysis

By running the python -m site command, the user output the current sys.path, which is the list of directories where Python looks for modules. The output shows a mix of Python 2.7 and Python 3.5 paths:

• Python 2.7 path: /opt/ros/indigo/lib/python2.7/dist-packages
• Python 3.5 paths: multiple directories starting with /home/omar/anaconda3/lib/python3.5

This mixed environment can lead to module loading confusion, as the glob module is part of the Python standard library, but different Python versions may have variations in its implementation or location. For example, the glob module for Python 2.7 might be in the standard library path, while the Anaconda environment for Python 3.5 might not be properly configured.

Solution: Installation Methods for Different Python Versions

According to the best answer, the key to resolving this error lies in distinguishing Python versions and using the correct package management tools. Here are the specific steps:

1. For Python 2.7 environments: Use the command pip install glob2 to install the glob2 package. glob2 is an enhanced version of the glob module, offering additional features such as recursive pattern matching. In Python 2.7, the standard library's glob module has limited functionality, and installing glob2 can extend its capabilities, but ensure that pip points to the Python 2.7 installer.
2. For Python 3.7 or later versions: Use the command pip3 install glob2. pip3 is the package installer for Python 3, ensuring that modules are installed into the correct Python 3 environment. In Python 3, the standard library's glob module is already quite robust, but glob2 still provides extra features like better performance or compatibility.

It is important to note that the user might have multiple Python versions installed, causing pip and pip3 to point to different interpreters. This can be verified by running pip --version and pip3 --version.

In-Depth Analysis: Why Installing glob2 Did Not Solve the Problem

The user mentioned that the error persisted after installing glob2, which could be due to the following reasons:

• Python version mismatch: If the pip command incorrectly points to a Python 3 environment while ROS Simulator runs on Python 2.7, the installed glob2 package will not be recognized by Python 2.7. From the sys.path output, the ROS path points to Python 2.7, and the Anaconda paths point to Python 3.5, increasing the risk of confusion.
• Module search path priority: Python searches for modules in the order specified in sys.path. If the standard library path (e.g., /usr/lib/python2.7) lacks the glob module, but the user-installed glob2 is in another path (e.g., site-packages), Python might still fail to find it, because import glob prioritizes finding a module named glob, not glob2.
• Environment variable configuration: The PYTHONPATH environment variable might not be set correctly, preventing Python from accessing installed modules. This is especially common in ROS environments, as ROS modifies Python paths to include its own packages.

Additional Recommendations and Best Practices

Beyond installing glob2, the following measures can help prevent and resolve similar issues:

• Use virtual environments: Create isolated Python virtual environments for ROS projects (e.g., using virtualenv or conda) to avoid version conflicts. For example, run conda create -n ros_env python=2.7 to create a Python 2.7 environment, then install required modules within it.
• Check module availability: Test if the module can be imported by running import glob in a Python interactive shell. If it fails, try import glob2 and ensure that import statements in the code are adjusted accordingly.
• Update system packages: Ensure that Python packages on the Ubuntu system are up-to-date. Run sudo apt-get update && sudo apt-get install python-glob2 (for Python 2.7) or use pip for installation.
• Refer to other answers: While the best answer provides direct installation commands, other answers might suggest checking Python paths or reconfiguring environments, which should be considered as supplementary references.

Conclusion

The core of resolving the ImportError: No module named 'glob' error lies in understanding Python's module system and version management. By correctly using pip or pip3 to install glob2, combined with environment configuration checks, developers can efficiently troubleshoot such issues. In mixed Python version environments, maintaining clear path management and using virtual environments are key to avoiding compatibility problems. Based on the user case, this article provides a complete guide from error analysis to solution, aiming to help readers quickly identify and fix problems in similar scenarios.