Credit: Robin Parmar
Modules must be on the Python search path before they can be imported, but you don’t want a huge permanent path, because that slows things down—you want to change the path dynamically.
We just conditionally
add a directory to Python’s
sys.path, carefully checking to avoid duplication:
def AddSysPath(new_path): """ AddSysPath(new_path): adds a directory to Python's sys.path Does not add the directory if it does not exist or if it's already on sys.path. Returns 1 if OK, -1 if new_path does not exist, 0 if it was already on sys.path. """ import sys, os # Avoid adding nonexistent paths if not os.path.exists(new_path): return -1 # Standardize the path. Windows is case-insensitive, so lowercase # for definiteness. new_path = os.path.abspath(new_path) if sys.platform == 'win32': new_path = new_path.lower( ) # Check against all currently available paths for x in sys.path: x = os.path.abspath(x) if sys.platform == 'win32': x = x.lower( ) if new_path in (x, x + os.sep): return 0 sys.path.append(new_path) return 1 if _ _name_ _ == '_ _main_ _': # Test and show usage import sys print 'Before:' for x in sys.path: print x if sys.platform == 'win32': print AddSysPath('c:\\Temp') print AddSysPath('c:\\temp') else: print AddSysPath('usr/lib/my_modules') print 'After:' for x in sys.path: print x
Modules must be on the Python search path before they can be
imported, but we don’t want to have a huge permanent
path, because that would slow down every import performed by every
Python script and application. This simple recipe dynamically adds a
directory to the path, but only if that directory exists and was not
sys.path is a list, so it’s easy
to add directories to its end, using
import performed after such an
append will automatically look in the newly added
directory, if it cannot be satisfied from earlier ones.
It’s no big problem if
ends up with some duplicates or if some nonexistent directory is
accidentally appended to it; Python’s
import statement is clever enough to shield itself
against such issues. However, each time such a problem occurs at
import time (from duplicate unsuccessful searches, errors from the
operating system that need to be handled gracefully, etc.), there is
a price to pay in terms of performance. To avoid the risk of these
performance issues, this recipe does a conditional addition to
sys.path, never appending any dictionary that
doesn’t exist or is already in
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