Sounds like a permissions issue with /usr/local.
### Makes you owner of /usr/local
$ sudo chown -R `whoami` /usr/local
### Force uninstalls failed python
$ brew uninstall -f python
### Clear the brew cache
$ rm -rf `brew --cache`
### Recreate the brew cache
$ mkdir `brew --cache`
### Cleanup - cleans up old homebrew files
$ brew cleanup
### Prune - removes dead symlinks in homebrew
$ brew prune
### Doctor - runs homebrew checks for common error causing issues
$ brew doctor
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### Google and follow steps to fix what `brew doctor` came back with
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### Reinstall python
$ brew install python