Is there a way in Python to check if an entry in os.environ is a variable or shell function?

Question

With the os module in Python, we can easily access environment variables through dict os.environ . However, I found that os.environ not only contains variables, but also globally defined shell functions (for example, from the module software package).

Is it possible from inside Python to find out if a given entry in os.environ is a function, not a variable? Note that a shell-agnostic solution is preferred , but I could justify a Bash-specific solution.

Answer 1

This bash function is specific, so checking the exported shell function should do what Bash does. The experiment and the source code show that Bash recognizes the environment variable as a shell function at startup due to the prefix () { in its value - if the prefix is ​​missing or even slightly changed, the variable is treated as a regular data variable.

Therefore, an equivalent Python check would look like this:

 def is_env_shell_func(name): return os.environ[name].startswith('() {') 

Answer 2

One solution that I find to work (but this is ridiculously clumsy) is this:

 import subprocess var = 'my_variable_name_i_want_to_check' p = subprocess.Popen('declare -f ' + var, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE) p.communicate() if p.returncode == 0: print('function') else: print('variable') 

Answer 3

Are you sure shell functions exist in os.environ?

 {master>}% function test_fn() { function> echo "Hello"; function> } {master>}% test_fn Hello {master>}% python Python 2.7.3 (default, Jan 2 2013, 13:56:14) [GCC 4.7.2] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import os >>> os.environ['test_fn'] Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/lib/python2.7/UserDict.py", line 23, in __getitem__ raise KeyError(key) KeyError: 'test_fn' >>> os.environ.keys() ['SSH_ASKPASS', 'PS_FORMAT', 'GIT_PS1_SHOWDIRTYSTATE', 'GNOME_DESKTOP_SESSION_ID', 'WINDOWPATH', 'LOGNAME', 'USER', 'GNOME_KEYRING_CONTROL', 'HOME', 'PS1', 'DISPLAY', 'PATH', 'LANG', 'TERM', 'SHELL', 'SSH_AGENT_PID', 'XAUTHORITY', 'LANGUAGE', 'GIT_PS1_SHOWSTASHSTATE', 'SHLVL', 'GIT_PS1_SHOWUPSTREAM', 'WINDOWID', 'EDITOR', 'MANPATH', 'GIT_PS1_SHOWCOLORHINTS', 'GPG_AGENT_INFO', 'USERNAME', 'WORKON_HOME', 'COLORTERM', 'WORDCHARS', 'SSH_AUTH_SOCK', 'TMUX', 'GDMSESSION', 'XDG_SESSION_COOKIE', 'LS_OPTIONS', 'DBUS_SESSION_BUS_ADDRESS', '_', 'VIRTUALENVWRAPPER_HOOK_DIR', 'VIRTUALENVWRAPPER_PROJECT_FILENAME', 'DESKTOP_SESSION', 'GIT_PS1_SHOWUNTRACKEDFILES', 'GNOME_KEYRING_PID', 'WINDOW_MANAGER', 'ZBEEP', 'PYTHONSTARTUP', 'OLDPWD', 'SESSION_MANAGER', 'XDG_DATA_DIRS', 'PWD', 'CFLAGS', 'VIRTUALENVWRAPPER_LOG_DIR', 'LS_COLORS', 'TMUX_PANE'] >>> DESKTOP_SESSION ',' GIT_PS1_SHOWUNTRACKEDFILES ',' GNOME_KEYRING_PID ',' WINDOW_MANAGER ',' ZBEEP ',' PYTHONSTARTUP ',' OLDPWD ',' SESSION_MANAGER ',' XDG_DATA_DIRS ',' PWD ',' CFLAGS ' {master>}% function test_fn() { function> echo "Hello"; function> } {master>}% test_fn Hello {master>}% python Python 2.7.3 (default, Jan 2 2013, 13:56:14) [GCC 4.7.2] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import os >>> os.environ['test_fn'] Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/lib/python2.7/UserDict.py", line 23, in __getitem__ raise KeyError(key) KeyError: 'test_fn' >>> os.environ.keys() ['SSH_ASKPASS', 'PS_FORMAT', 'GIT_PS1_SHOWDIRTYSTATE', 'GNOME_DESKTOP_SESSION_ID', 'WINDOWPATH', 'LOGNAME', 'USER', 'GNOME_KEYRING_CONTROL', 'HOME', 'PS1', 'DISPLAY', 'PATH', 'LANG', 'TERM', 'SHELL', 'SSH_AGENT_PID', 'XAUTHORITY', 'LANGUAGE', 'GIT_PS1_SHOWSTASHSTATE', 'SHLVL', 'GIT_PS1_SHOWUPSTREAM', 'WINDOWID', 'EDITOR', 'MANPATH', 'GIT_PS1_SHOWCOLORHINTS', 'GPG_AGENT_INFO', 'USERNAME', 'WORKON_HOME', 'COLORTERM', 'WORDCHARS', 'SSH_AUTH_SOCK', 'TMUX', 'GDMSESSION', 'XDG_SESSION_COOKIE', 'LS_OPTIONS', 'DBUS_SESSION_BUS_ADDRESS', '_', 'VIRTUALENVWRAPPER_HOOK_DIR', 'VIRTUALENVWRAPPER_PROJECT_FILENAME', 'DESKTOP_SESSION', 'GIT_PS1_SHOWUNTRACKEDFILES', 'GNOME_KEYRING_PID', 'WINDOW_MANAGER', 'ZBEEP', 'PYTHONSTARTUP', 'OLDPWD', 'SESSION_MANAGER', 'XDG_DATA_DIRS', 'PWD', 'CFLAGS', 'VIRTUALENVWRAPPER_LOG_DIR', 'LS_COLORS', 'TMUX_PANE'] >>>