When a module named spam is imported, the interpreter first searches for a built-in module with that name. If not found, it then searches for a file named spam.py in a list of directories given by the variable sys.path. sys.path is initialized from these locations:

• The directory containing the input script (or the current directory when no file is specified).

• PYTHONPATH (a list of directory names, with the same syntax as the shell variable PATH).

• The installation-dependent default.

当导入名为spam的模块时，解释器首先搜索具有该名称的内置模块。如果没有找到，它会搜索一个名为spam.py的文件。变量sys.path. sys给出的目录列表中的py。路径是从这些位置初始化的:

• 包含输入脚本的目录(或未指定文件时的当前目录)。
• PYTHONPATH(一个目录名列表，与shell变量PATH具有相同的语法)。
• installation-dependent默认。

Note：On file systems which support symlinks, the directory containing the input script is calculated after the symlink is followed. In other words the directory containing the symlink is not added to the module search path.

After initialization, Python programs can modify sys.path. The directory containing the script being run is placed at the beginning of the search path, ahead of the standard library path. This means that scripts in that directory will be loaded instead of modules of the same name in the library directory. This is an error unless the replacement is intended. See section Standard Modules for more information.