The 2to3 command is used to convert Python 2.x code to Python 3.x code, automating the necessary changes required for the transition. It eliminates the need for manual code modifications and saves time when upgrading codebases.

Use case 1: Display the changes that would be performed without performing them (dry-run)

Code:

2to3 path/to/file.py

Motivation: This use case is helpful when you want to see the changes that would be made to a Python 2 file before performing the actual conversion. It allows you to review the modifications and ensure that they align with your intentions.

Explanation:

• 2to3: The command to initiate the code conversion.
• path/to/file.py: The location of the Python 2 file to be converted.

Example output:

RefactoringTool: Files to be modified:
RefactoringTool: path/to/file.py
RefactoringTool: No changes to path/to/file.py

Use case 2: Convert a Python 2 file to Python 3

Code:

2to3 --write path/to/file.py

Motivation: This use case is used when you want to convert a Python 2 file to Python 3 directly, without a dry run. It modifies the file in place and updates the code according to the 2to3 conversion rules.

Explanation:

• 2to3: The command to initiate the code conversion.
• --write: Instructs 2to3 to write the changes directly to the file. Without this flag, 2to3 will only perform a dry run and not modify the original file.
• path/to/file.py: The location of the Python 2 file to be converted.

Example output (before conversion):

# Python 2 code
print("Hello, World!")

Example output (after conversion):

# Python 3 code
print("Hello, World!")

Use case 3: Convert specific Python 2 language features to Python 3

Code:

2to3 --write path/to/file.py --fix=raw_input --fix=print

Motivation: Sometimes, you may want to convert specific language features from Python 2 to Python 3. This use case shows how to convert the raw_input and print statements specifically.

Explanation:

• 2to3: The command to initiate the code conversion.
• --write: Instructs 2to3 to write the changes directly to the file.
• --fix=raw_input --fix=print: Specifies the specific language features to fix. In this case, it converts raw_input statements to input and print statements to the appropriate Python 3 syntax.

Example output (before conversion):

# Python 2 code
name = raw_input("Enter your name: ")
print "Hello,", name

Example output (after conversion):

# Python 3 code
name = input("Enter your name: ")
print("Hello,", name)

Use case 4: Convert all Python 2 language features except the specified ones to Python 3

Code:

2to3 --write path/to/file.py --nofix=has_key --nofix=isinstance

Motivation: There might be cases where you want to convert all Python 2 features to Python 3, except for a few specific ones. This use case shows how to exclude the has_key and isinstance fixes from the conversion.

Explanation:

• 2to3: The command to initiate the code conversion.
• --write: Instructs 2to3 to write the changes directly to the file.
• --nofix=has_key --nofix=isinstance: Specifies the specific language features to exclude from the conversion. In this case, it does not modify has_key and isinstance statements.

Example output (before conversion):

# Python 2 code
dict = {'name': 'John'}
if dict.has_key('name'):
    print(isinstance(dict['name'], str))

Example output (after conversion):

# Python 3 code
dict = {'name': 'John'}
if dict.has_key('name'):
    print(isinstance(dict['name'], str))

Use case 5: Display a list of all available language features that can be converted from Python 2 to Python 3

Code:

2to3 --list-fixes

Motivation: This use case allows you to view the complete list of available language feature fixes that 2to3 can perform. It gives you an overview of what changes will be made during the conversion process.

Explanation:

• 2to3: The command to initiate the code conversion.
• --list-fixes: Instructs 2to3 to display a list of all available language feature fixes without performing any conversions.

Example output:

Available transformations for the -x flag:
apply
basestring
buffer
...

Use case 6: Convert all Python 2 files in a directory to Python 3

Code:

2to3 --output-dir=path/to/python3_directory --write-unchanged-files --nobackups path/to/python2_directory

Motivation: This use case is helpful when you want to convert all Python 2 files in a directory to Python 3 and save the converted files in a separate directory. It also ensures that the original Python 2 files remain unchanged and removes any backup files created during the conversion.

Explanation:

• 2to3: The command to initiate the code conversion.
• --output-dir=path/to/python3_directory: Specifies the directory to save the converted Python 3 files.
• --write-unchanged-files: Instructs 2to3 to write the unchanged Python 2 files to the output directory.
• --nobackups: Prevents 2to3 from creating backup files during the conversion process.
• path/to/python2_directory: The location of the directory containing the Python 2 files to be converted.

Example directory structure (before conversion):

• path/to/python2_directory
  • script1.py
  • script2.py

Example directory structure (after conversion):

• path/to/python2_directory
  • script1.py
  • script2.py
• path/to/python3_directory
  • script1.py
  • script2.py

Use case 7: Run 2to3 with multiple threads

Code:

2to3 --processes=4 --output-dir=path/to/python3_directory --write --nobackups --no-diff path/to/python2_directory

Motivation: When dealing with a large number of Python 2 files, running 2to3 with multiple threads can speed up the conversion process. This use case demonstrates how to use multiple threads to convert files and save the converted files to a separate directory, without creating backup files or generating diff files.

Explanation:

• 2to3: The command to initiate the code conversion.
• --processes=4: Specifies the number of threads to use during the conversion. In this case, 4 threads are used.
• --output-dir=path/to/python3_directory: Specifies the directory to save the converted Python 3 files.
• --write: Instructs 2to3 to write the changes directly to the file.
• --nobackups: Prevents 2to3 from creating backup files during the conversion process.
• --no-diff: Skips generating diff files for the changes made during the conversion process.
• path/to/python2_directory: The location of the directory containing the Python 2 files to be converted.

Example directory structure (before conversion):

• path/to/python2_directory
  • script1.py
  • script2.py
  • script3.py
  • script4.py

Example directory structure (after conversion):

• path/to/python2_directory
  • script1.py
  • script2.py
  • script3.py
  • script4.py
• path/to/python3_directory
  • script1.py
  • script2.py
  • script3.py
  • script4.py

Conclusion:

The 2to3 command is a versatile tool that enables seamless migration of Python 2 codebases to Python 3. With its various options and flexible usage, developers can effectively and efficiently convert their legacy code to the latest Python version with minimal effort. Whether it is converting specific language features or running multiple conversions in parallel, 2to3 simplifies the transition process and ensures code compatibility during the migration.