#每次执行脚本时，python会将执行脚本目录加入PYTHONPATH环境变量中(sys.path获取)
#!/usr/bin/python3

import os
import sys

print(sys.path)
print(sys.path[0])
执行结果：
[root@localhost tmp]# ./py_test1/pytest24.py 
[‘/tmp/py_test1‘, ‘/usr/local/lib/python36.zip‘, ‘/usr/local/lib/python3.6‘, ‘/usr/local/lib/python3.6/lib-dynload‘, ‘/usr/local/lib/python3.6/site-packages‘, ‘/usr/local/lib/python3.6/site-packages/pip-9.0.1-py3.6.egg‘]
/tmp/py_test1

#!/usr/bin/python3

import os
import sys

print(sys.argv[0])
执行1结果：
[root@localhost tmp]# ./py_test1/pytest24.py 　　#相对路径执行脚本则会返回相对路径
./py_test1/pytest24.py
执行2结果：
[root@localhost tmp]# /tmp/py_test1/pytest24.py  #绝对路径执行脚本则返回绝对路径
/tmp/py_test1/pytest24.py

#!/usr/bin/python3

import os
import sys

print("sys.argv[0] Output:",sys.argv[0])
print("__file Output:",__file__)
执行1结果：
[root@localhost tmp]# ./py_test1/pytest24.py   #相对路径执行脚本则会返回相对路径
sys.argv[0] Output: ./py_test1/pytest24.py
__file Output: ./py_test1/pytest24.p

执行2结果：
[root@localhost tmp]# /tmp/py_test1/pytest24.py  #绝对路径执行脚本则会返回绝对路径
sys.argv[0] Output: /tmp/py_test1/pytest24.py
__file Output: /tmp/py_test1/pytest24.py

#!/usr/bin/python3

import os
import sys

print("__file Output:",__file__)
print(os.path.abspath(__file__))
print(os.path.realpath(__file__))
执行结果：
[root@localhost tmp]# ./py_test1/pytest24.py 
__file Output: ./py_test1/pytest24.py
/tmp/py_test1/pytest24.py
/tmp/py_test1/pytest24.py