How to obtain a Thread id in Python?

Question

I have a multi-threading Python program, and a utility function, writeLog(message), that writes out a timestamp followed by the message. Unfortunately, the resultant log file gives no indication of which thread is generating which message.

I would like writeLog() to be able to add something to the message to identify which thread is calling it. Obviously I could just make the threads pass this information in, but that would be a lot more work. Is there some thread equivalent of os.getpid() that I could use?

Answer 1

threading.get_ident() works, or threading.current_thread().ident (or threading.currentThread().ident for Python < 2.6).

Answer 2

Using the logging module you can automatically add the current thread identifier in each log entry. Just use one of these LogRecord mapping keys in your logger format string:

%(thread)d : Thread ID (if available).

%(threadName)s : Thread name (if available).

and set up your default handler with it:

logging.basicConfig(format="%(threadName)s:%(message)s")

Answer 3

This functionality is now supported by Python 3.8+ :)

You can now use: threading.get_native_id()

https://github.com/python/cpython/commit/4959c33d2555b89b494c678d99be81a65ee864b0

https://github.com/python/cpython/pull/11993

Answer 4

The thread.get_ident() function returns a long integer on Linux. It's not really a thread id.

I use this method to really get the thread id on Linux:

import ctypes
libc = ctypes.cdll.LoadLibrary('libc.so.6')

# System dependent, see e.g. /usr/include/x86_64-linux-gnu/asm/unistd_64.h
SYS_gettid = 186

def getThreadId():
   """Returns OS thread id - Specific to Linux"""
   return libc.syscall(SYS_gettid)

Answer 5

You can get the ident of the current running thread. The ident could be reused for other threads, if the current thread ends.

When you crate an instance of Thread, a name is given implicit to the thread, which is the pattern: Thread-number

The name has no meaning and the name don't have to be unique. The ident of all running threads is unique.

import threading


def worker():
    print(threading.current_thread().name)
    print(threading.get_ident())


threading.Thread(target=worker).start()
threading.Thread(target=worker, name='foo').start()

The function threading.current_thread() returns the current running thread. This object holds the whole information of the thread.

Answer 6

I saw examples of thread IDs like this:

class myThread(threading.Thread):
    def __init__(self, threadID, name, counter):
        self.threadID = threadID
        ...

The threading module docs lists name attribute as well:

...

A thread has a name. 
The name can be passed to the constructor, 
and read or changed through the name attribute.

...

Thread.name

A string used for identification purposes only. 
It has no semantics. Multiple threads may
be given the same name. The initial name is set by the constructor.

Answer 7

I created multiple threads in Python, I printed the thread objects, and I printed the id using the ident variable. I see all the ids are same:

<Thread(Thread-1, stopped 140500807628544)>
<Thread(Thread-2, started 140500807628544)>
<Thread(Thread-3, started 140500807628544)>

Answer 8

Similarly to @brucexin I needed to get OS-level thread identifier (which != thread.get_ident()) and use something like below not to depend on particular numbers and being amd64-only:

---- 8< ---- (xos.pyx)
"""module xos complements standard module os""" 

cdef extern from "<sys/syscall.h>":                                                             
    long syscall(long number, ...)                                                              
    const int SYS_gettid                                                                        

# gettid returns current OS thread identifier.                                                  
def gettid():                                                                                   
    return syscall(SYS_gettid)                                                                  

and

---- 8< ---- (test.py)
import pyximport; pyximport.install()
import xos

...

print 'my tid: %d' % xos.gettid()

this depends on Cython though.