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A forewarning

While Python and SCons are compatible with one another they are not completely interchangeable. To understand why that is the case, you need to understand the underlying design of SCons. SCons is a declarative language, which means that you tell SCons what to do through the: Flow, Plot, and Result commands, and then SCons decides how and when to execute those commands. Python on the other hand is imperative, which means that as Python reads a Python script, it executes the commands immediately. Python does not take time to decide how or when to execute your commands. This point causes a bit of confusion to users who start to combine Python and SCons together because they expect SCons commands to execute in the order that they place them, which is not the case. Because of this, you may not be able to use certain Python features in their native Python way. For example, loops which require repeated computation, and whose results depend on the result of the last iteration are not possible using SCons. It is also not usually possible to use Python variables that change during execution with SCons because the variable value that SCons will use is always the last value of the variable. Typically, you cannot use conditional statements in SCons, where the choice depends on a file that SCons will build.

To be safe, you should always assume that whatever Python does happens before SCons starts running commands.

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