where does the welcome message of interactive python interpreter come from?

Question

When entering python on Linux shell, the welcome message is printed:

[root@localhost ~]# python
Python 2.7.5 (default, Nov 20 2015, 02:00:19)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.

where do those lines come from? Are they determined during compilation or installation?

I have another version of python executable and a set of libs on my system, but when I enter that python, it also shows the same welcome message as above.

Thanks,

UPDATE:

I use absolute path to start another version of python. And just found the welcome message has the same content as sys.version and sys.platform. But if I copy the other version of python to a different Linux machine B, and still use absolute path to run it. I get

Python 2.7.15rc1 (default, Nov 12 2018, 14:31:15)
[GCC 7.3.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.

This welcome message is the same as machine B's python.

Not sure why this has been downvoted. Not the most fantastically interesting, maybe, but I have no idea where it comes from. — roganjosh, Nov 21 '18 at 19:43
Half of it will be due to your `PATH` as to which version of python you are calling. Is your question less about what generates that output and more about how to invoke a particular python interpreter? — roganjosh, Nov 21 '18 at 19:46
did you check if "when you enter the other one" you arenot actually calling the same one - due to pathing, symlinks or whatever?# — Patrick Artner, Nov 21 '18 at 19:46
@roganjosh and patrick artner, I just updated. I used absolute path to run the other python. — password636, Nov 21 '18 at 20:19

William Chong · Answer 1 · 2018-11-21T19:59:30.033

1

Edited: The C version source code is similar: https://github.com/python/cpython/blob/7e4db2f253c555568d56177c2fd083bcf8f88d34/Modules/main.c#L705

if (!Py_QuietFlag && (Py_VerboseFlag ||
                    (command == NULL && filename == NULL &&
                     module == NULL && stdin_is_interactive))) {
    fprintf(stderr, "Python %s on %s\n",
        Py_GetVersion(), Py_GetPlatform());
    if (!Py_NoSiteFlag)
        fprintf(stderr, "%s\n", COPYRIGHT);
}

which Py_GetVersion() returns version base on a MACRO

https://github.com/python/cpython/blob/7e4db2f253c555568d56177c2fd083bcf8f88d34/Include/patchlevel.h#L26

/* Version as a string */
#define PY_VERSION          "3.7.0a0"

so it is compile time determined, you probably have a messed up PATH?

Old answer, which is actually just a python module

https://github.com/python/cpython/blob/7e4db2f253c555568d56177c2fd083bcf8f88d34/Lib/code.py#L214

    if banner is None:
        self.write("Python %s on %s\n%s\n(%s)\n" %
                   (sys.version, sys.platform, cprt,
                    self.__class__.__name__))
    elif banner:
        self.write("%s\n" % str(banner))

Not sure if this answers your question, but still fun to know.

edited Nov 21 '18 at 19:59

answered Nov 21 '18 at 19:45

William Chong

2,107
13
24

That's the `code` module, not the actual implementation of interactive mode, though. – user2357112 Nov 21 '18 at 19:47
You're looking at the C now, but the wrong part of the C. What you're looking at is part of the handling for `python --version`, not the interactive header. – user2357112 Nov 21 '18 at 19:55
well screw me, updated again Lol... Hope I get it right this time – William Chong Nov 21 '18 at 20:00
@user2357112 I'm curious why you're not answering this one? – roganjosh Nov 21 '18 at 20:22
1

@roganjosh: I've got most of an answer written up, but the newest revision of this answer is finally using the right source code, so I didn't bother posting it. – user2357112 Nov 21 '18 at 20:24

score 1 · Answer 2 · answered Nov 23 '18 at 07:44

I've finally found the reason. The second python binary loads .so files in startup, and it loads libpython as follows:

libpython2.7.so.1.0 => /lib64/libpython2.7.so.1.0 (0x00007f087cf58000)

This is the same as my system python. After setting LD_LIBRARY_PATH to the lib directory of the second python, I can see the correct welcome message.

where does the welcome message of interactive python interpreter come from?

2 Answers2

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