[More setup and build instructions specifically for code contributors, building on the basics from the :ref:`Getting Started <getting-started>` section.]
When running ./configure, CPython performs a series of system checks, which can take time. To speed up repeated builds, you can use the configure cache, which saves previous results:
./configure -C### Benefits - Faster rebuilds: Avoids redundant system checks, making subsequent runs quicker. - Improves development workflow: Speeds up the edit-configure-build-test cycle, especially for frequent changes. - Reduces CPU and disk usage: Skips unnecessary recomputation of configuration results.
### Clearing the Cache If you modify system settings, upgrade dependencies, or suspect cache-related issues, clear the cache before reconfiguring to avoid outdated settings:
rm -f config.cacheThis ensures that ./configure runs fresh system checks when necessary.
### When to Use `configure -C` - Use it when making minor code changes that don’t affect system dependencies. - Avoid it after system updates, compiler changes, or dependency modifications to prevent build inconsistencies.
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### Why This Additional Detail? - The `-C` flag behavior: Makes it clear when to use or avoid it. - Cache clearing instructions: Important to prevent build failures due to stale configuration data. - More structured benefits: Helps new contributors understand why they should use it.
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### Overview
When running ./configure, CPython performs a series of system checks to detect available features, libraries, and compiler options. These checks help generate a proper Makefile for building CPython. However, a fresh configuration scan can take significant time, especially on slower systems or when running it frequently during development.
To optimize this process, you can use the configure cache (configure -C), which saves the results of previous runs and reuses them for subsequent configurations.
./configure -CBy caching detected system properties, this approach eliminates redundant checks, making reconfigurations significantly faster.
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### Benefits of Using Configure Cache
Using configure -C can enhance the development workflow in multiple ways:
- Speeds up rebuilds: Avoids rechecking system dependencies, making incremental changes quicker.
- Reduces system load: Skips redundant computations, lowering CPU usage.
- Improves iteration time: Speeds up the edit-configure-build-test cycle, especially for developers frequently modifying CPython’s internals.
- Ensures consistency: Maintains uniform configuration settings across multiple runs unless the cache is explicitly cleared.
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### When to Use `configure -C`?
|----------------------------------------------|-----------------|------------------------------------------------| | Small code changes (e.g., modifying .c files) | ✅ Yes | Avoids unnecessary reconfiguration steps. | | Frequent rebuilds without system changes | ✅ Yes | Saves time and system resources. | | Upgrading system libraries (e.g., OpenSSL) | ❌ No | Cache may store outdated results, leading to inconsistencies. | | Changing compiler settings or flags | ❌ No | A fresh ./configure run is needed to reflect changes. | | Switching between Python build environments | ❌ No | Using cache might introduce conflicts between builds. |
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### Clearing the Configure Cache
If you have modified system settings, upgraded dependencies, or changed compiler options, it's recommended to clear the cache before re-running ./configure to avoid build inconsistencies.
To remove the cached configuration results, use:
rm -f config.cacheThis ensures that ./configure performs a fresh system scan, preventing potential errors due to stale configuration data.
Best Practice: If you encounter unexpected build issues after using configure -C, try clearing the cache first before debugging further.
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### Additional Notes
- configure -C only caches successful test results. If a check fails, it will still be re-run in subsequent configurations.
- Some system changes might not require clearing the cache, but if in doubt, it's safer to remove it.
- The cache is stored in config.cache in the build directory and is automatically used if present when configure -C is executed.
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### Summary
- ./configure -C caches system checks to speed up rebuilds.
- Recommended for frequent code changes but not for system or compiler updates.
- Clear the cache using rm -f config.cache when necessary.
By following these guidelines, you can make the most out of configure -C while ensuring stable and efficient builds.
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