Just wondering why
import sys
exit(0)
gives me this error:
Traceback (most recent call last):
File "<pyshell#1>", line 1, in ?
exit(0)
TypeError: 'str' object is not callable
but
from sys import exit
exit(0)
works fine?
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How are you getting the first error. For me in a script it just exits with no printoutmmmmmm– mmmmmm2010-06-08 12:27:37 +00:00Commented Jun 8, 2010 at 12:27
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1Probably running a script and not interactive mode. exit() is a special interactive mode command.FogleBird– FogleBird2010-06-08 12:28:54 +00:00Commented Jun 8, 2010 at 12:28
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Maybe it exits before you can see the printout. You try running it in IDLE?Richard– Richard2010-06-08 12:54:03 +00:00Commented Jun 8, 2010 at 12:54
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3 Answers
Python imports only the chosen names into the namespace.
Your equivalent first solution should be
sys.exit(0)
since import sys imports only the sys keyword into the current namespace.
Comments
See http://effbot.org/zone/import-confusion.htm for all the different ways to use import in Python.
import sys
This imports the sys module and binds it to the name "sys" in your namespace. "exit", and other members of the sys module are not brought into the namespace directly but can be accessed like so:
sys.exit(0)
from sys import exit
This imports specific members of the sys module into your namespace. Specifically this binds the name "exit" to the sys.exit function.
exit(0)
To see what's in your namespace, use the dir function.
>>> import sys
>>> dir()
['__builtins__', '__doc__', '__name__', '__package__', 'sys']
>>>
>>> from sys import exit
>>> dir()
['__builtins__', '__doc__', '__name__', '__package__', 'exit', 'sys']
You can even see what all is in the sys module itself:
>>> dir(sys)
['__displayhook__', '__doc__', '__egginsert', '__excepthook__', '__name__', '__package__', '__plen', '__stderr__', '__stdin__', '__stdout__', '_clear_type_cache', '_current_frames', '_getframe', 'api_version', 'argv', 'builtin_module_names', 'byteorder', 'call_tracing', 'callstats', 'copyright', 'displayhook', 'dllhandle', 'dont_write_bytecode', 'exc_clear', 'exc_info', 'exc_type', 'excepthook', 'exec_prefix', 'executable', 'exit', 'flags', 'float_info', 'getcheckinterval', 'getdefaultencoding', 'getfilesystemencoding', 'getprofile', 'getrecursionlimit', 'getrefcount', 'getsizeof', 'gettrace', 'getwindowsversion', 'hexversion', 'maxint', 'maxsize', 'maxunicode', 'meta_path', 'modules', 'path', 'path_hooks', 'path_importer_cache', 'platform', 'prefix', 'ps1', 'ps2', 'py3kwarning', 'setcheckinterval', 'setprofile', 'setrecursionlimit', 'settrace', 'stderr', 'stdin', 'stdout', 'subversion', 'version', 'version_info', 'warnoptions', 'winver']
Comments
Ok from your Answers I can remeber that:
import sys from *
would import all members from sys
3 Comments
Wayne Werner
This is, of course, discouraged because it produces namespace pollution. The script
print len(locals()); from sys import *; print len(locals()) produces 4 and then 47 as the local variable count. This is undesirable for several reasons, the main being increased likelihood that your name shadows an imported name. Though for one-off scripts and testing it's not horrible, but as a general rule it should be avoided.
Richard
Yeah I agree with what you are saying Wayne. It could lead to unexpected results. This is why I named Lakshman Prasad answer as number one. Maybe I should not have included this answer in case it confuses others. Thanks for clarifying
Mike Graham
1) The syntax is
from sys import * (you have the keywords backwards), and 2) Never ever ever use this feature.