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Installing and Upgrading Packages

With the RPM system, you have a lot of choices. You can install or upgrade packages with the rpm command. You can install or upgrade packages with special programs you write using the C API. And you can install or upgrade packages using the Python API. If you are writing a special program to install or upgrade packages, the Python API makes this task much easier. As with the C API, most of your work needs to be part of a transaction set.
To install or upgrade a package, you need to create a transaction set, build up the transaction with packages, which are stored as transaction elements within the transaction set, check for unresolved dependencies, reorder the transaction set based on the dependencies, and then run the transaction set. Running the transaction set installs or upgrades the packages. The following sections cover these steps.

Building up the transaction set

Package installs and upgrades need to be performed within the context of a transaction set. To install or upgrade a set of packages, you need to call addInstall with the package headers to install or upgrade. The basic syntax follows:
ts.addInstall(header, key_data, mode)
When you call addInstall, you pass the header object along with arbitrary callback key data and a mode flag. The mode flag should be 'i' to install a package, 'u' to upgrade a package, or 'a' as a special code to make a package available for transaction checks but not install or upgrade the package. The 'a' flag is rarely used. In most cases, you should use 'u', just as in most cases, you should install packages with rpm –U instead of rpm –i.
The key_data parameter will get passed to the transaction set run callback, covered in the “Running the Transaction” section later in this chapter.
To remove packages instead of install or upgrade, call addErase instead of addInstall:
To set up a package to be upgraded or installed, you can use code like the following:
h = readRpmHeader( ts, sys.argv[1] )
ts.addInstall(h, sys.argv[1], 'u')
This example expects a package file name on the command line (accessed with sys.argv[1]), and reads in the package header using the readRpmHeader function introduced previously.
The call to addInstall adds the header object (and the associated RPM package file) for an upgrade with the 'u' mode flag. The name of the package file, from sys.argv[1], is passed as the arbitrary data for the transaction set run callback function.