CODEWITHSUNDEEP
python
password636
password636

Reputation: 1011

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

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.

Upvotes: 1

Views: 352

Answers (2)

password636
password636

Reputation: 1011

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.

Upvotes: 1

William Chong
William Chong

Reputation: 2203

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.

Upvotes: 1

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