Update Aug. 2022:

In modern Python 3, import time followed by time.monotonic_ns() might be sufficient. See my new answer to this other question here: High-precision clock in Python. At the time of my answer in 2016 using Python 3.1 on a Raspberry Pi, that didn’t exist.

See https://docs.python.org/3/library/time.html#time.monotonic_ns. This is new in Python 3.7. I haven’t tested it myself yet though. Thanks for @HenrikMadsen for posting this in his answer here, which he since deleted, unfortunately.

I still need to test these new Python 3.7 and later functions to see if they are as good as what I have below.

So, try this first and compare it to what I have done below:

import time

time_ns = time.monotonic_ns()

You might also try time.clock_gettime_ns() on Unix or Linux systems. Based on its name, it appears to call the underlying clock_gettime() C function which I use in my nanos() function in C in my answer here and in my C Unix/Linux library here: timinglib.c.

---

Original answer in 2016:

Here’s a fully-functional module for both Linux and Windows, and which is unique from all other answers here in that it works in pre-Python 3.3. All other answers there require Python 3.7 or later in most cases, and Python 3.3 or later in other cases. Again, my answer below works in Windows and Linux in any version of Python, going back at least as early as Python 3.0 or so, in case you need that (I can’t remember if it works on Python 2.7 or not).

It uses the ctypes library to call C or C++ dynamic libraries in Python via .dll "dynamically linked library" files in Windows, or .so "shared object" library files in Unix or Linux.

Functions and code samples.
Functions include:

• micros()
• millis()
• delay()
• delayMicroseconds()

Download GS_timing.py from my eRCaGuy_PyTime repo, then do:

import GS_timing

time_ms = GS_timing.millis()
time_us = GS_timing.micros()
GS_timing.delay(10)                # delay 10 ms
GS_timing.delayMicroseconds(10000) # delay 10000 us

Python code module (on GitHub as eRCaGuy_PyTime):

"""
GS_timing.py
-create some low-level Arduino-like millis() (milliseconds) and micros() 
 (microseconds) timing functions for Python 
By Gabriel Staples
http://www.ElectricRCAircraftGuy.com 
-click "Contact me" at the top of my website to find my email address 
Started: 11 July 2016 
Updated: 13 Aug 2016 

History (newest on top): 
20160813 - v0.2.0 created - added Linux compatibility, using ctypes, so that it's compatible with pre-Python 3.3 (for Python 3.3 or later just use the built-in time functions for Linux, shown here: https://docs.python.org/3/library/time.html)
-ex: time.clock_gettime(time.CLOCK_MONOTONIC_RAW)
20160711 - v0.1.0 created - functions work for Windows *only* (via the QPC timer)

References:
WINDOWS:
-personal (C++ code): GS_PCArduino.h
1) Acquiring high-resolution time stamps (Windows)
   -https://msdn.microsoft.com/en-us/library/windows/desktop/dn553408(v=vs.85).aspx
2) QueryPerformanceCounter function (Windows)
   -https://msdn.microsoft.com/en-us/library/windows/desktop/ms644904(v=vs.85).aspx
3) QueryPerformanceFrequency function (Windows)
   -https://msdn.microsoft.com/en-us/library/windows/desktop/ms644905(v=vs.85).aspx
4) LARGE_INTEGER union (Windows)
   -https://msdn.microsoft.com/en-us/library/windows/desktop/aa383713(v=vs.85).aspx

-*****https://stackoverflow.com/questions/4430227/python-on-win32-how-to-get-
absolute-timing-cpu-cycle-count
   
LINUX:
-https://stackoverflow.com/questions/1205722/how-do-i-get-monotonic-time-durations-in-python


"""

import ctypes, os 

#Constants:
VERSION = '0.2.0'

#-------------------------------------------------------------------
#FUNCTIONS:
#-------------------------------------------------------------------
#OS-specific low-level timing functions:
if (os.name=='nt'): #for Windows:
    def micros():
        "return a timestamp in microseconds (us)"
        tics = ctypes.c_int64()
        freq = ctypes.c_int64()

        #get ticks on the internal ~2MHz QPC clock
        ctypes.windll.Kernel32.QueryPerformanceCounter(ctypes.byref(tics)) 
        #get the actual freq. of the internal ~2MHz QPC clock
        ctypes.windll.Kernel32.QueryPerformanceFrequency(ctypes.byref(freq))  
        
        t_us = tics.value*1e6/freq.value
        return t_us
        
    def millis():
        "return a timestamp in milliseconds (ms)"
        tics = ctypes.c_int64()
        freq = ctypes.c_int64()

        #get ticks on the internal ~2MHz QPC clock
        ctypes.windll.Kernel32.QueryPerformanceCounter(ctypes.byref(tics)) 
        #get the actual freq. of the internal ~2MHz QPC clock 
        ctypes.windll.Kernel32.QueryPerformanceFrequency(ctypes.byref(freq)) 
        
        t_ms = tics.value*1e3/freq.value
        return t_ms

elif (os.name=='posix'): #for Linux:

    #Constants:
    CLOCK_MONOTONIC_RAW = 4 # see <linux/time.h> here: https://github.com/torvalds/linux/blob/master/include/uapi/linux/time.h
    
    #prepare ctype timespec structure of {long, long}
    class timespec(ctypes.Structure):
        _fields_ =
        [
            ('tv_sec', ctypes.c_long),
            ('tv_nsec', ctypes.c_long)
        ]
        
    #Configure Python access to the clock_gettime C library, via ctypes:
    #Documentation:
    #-ctypes.CDLL: https://docs.python.org/3.2/library/ctypes.html
    #-librt.so.1 with clock_gettime: https://docs.oracle.com/cd/E36784_01/html/E36873/librt-3lib.html #-
    #-Linux clock_gettime(): http://linux.die.net/man/3/clock_gettime
    librt = ctypes.CDLL('librt.so.1', use_errno=True)
    clock_gettime = librt.clock_gettime
    #specify input arguments and types to the C clock_gettime() function
    # (int clock_ID, timespec* t)
    clock_gettime.argtypes = [ctypes.c_int, ctypes.POINTER(timespec)]

    def monotonic_time():
        "return a timestamp in seconds (sec)"
        t = timespec()
        #(Note that clock_gettime() returns 0 for success, or -1 for failure, in
        # which case errno is set appropriately)
        #-see here: http://linux.die.net/man/3/clock_gettime
        if clock_gettime(CLOCK_MONOTONIC_RAW , ctypes.pointer(t)) != 0:
            #if clock_gettime() returns an error
            errno_ = ctypes.get_errno()
            raise OSError(errno_, os.strerror(errno_))
        return t.tv_sec + t.tv_nsec*1e-9 #sec 
    
    def micros():
        "return a timestamp in microseconds (us)"
        return monotonic_time()*1e6 #us 
        
    def millis():
        "return a timestamp in milliseconds (ms)"
        return monotonic_time()*1e3 #ms 

#Other timing functions:
def delay(delay_ms):
    "delay for delay_ms milliseconds (ms)"
    t_start = millis()
    while (millis() - t_start < delay_ms):
      pass #do nothing 
    return

def delayMicroseconds(delay_us):
    "delay for delay_us microseconds (us)"
    t_start = micros()
    while (micros() - t_start < delay_us):
      pass #do nothing 
    return 
        
#-------------------------------------------------------------------
#EXAMPLES:
#-------------------------------------------------------------------
#Only executute this block of code if running this module directly,
#*not* if importing it
#-see here: http://effbot.org/pyfaq/tutor-what-is-if-name-main-for.htm
if __name__ == "__main__": #if running this module as a stand-alone program

    #print loop execution time 100 times, using micros()
    tStart = micros() #us
    for x in range(0, 100):
        tNow = micros() #us
        dt = tNow - tStart #us; delta time 
        tStart = tNow #us; update 
        print("dt(us) = " + str(dt))

    #print loop execution time 100 times, using millis()
    print("n")
    tStart = millis() #ms
    for x in range(0, 100):
        tNow = millis() #ms
        dt = tNow - tStart #ms; delta time 
        tStart = tNow #ms; update 
        print("dt(ms) = " + str(dt))
        
    #print a counter once per second, for 5 seconds, using delay 
    print("nstart")
    for i in range(1,6):
        delay(1000)
        print(i)

    #print a counter once per second, for 5 seconds, using delayMicroseconds
    print("nstart")
    for i in range(1,6):
        delayMicroseconds(1000000)
        print(i)

If you know how to get the above millisecond and microsecond-resolution timestamps in Linux, please post, as that would be very helpful too.

This works for Linux too, including in pre-Python 3.3, since I’m using C functions via the ctypes module in order to read the time stamps.

(Note: code above originally posted here: http://www.electricrcaircraftguy.com/2016/07/arduino-like-millisecond-and-microsecond-timestamps-in-python.html)

Special thanks to @ArminRonacher for his brilliant pre-Python 3.3 Linux answer here: https://stackoverflow.com/a/1205762/4561887

Timestamp and clock references:

1. Windows: QueryPerformanceCounter(): https://docs.microsoft.com/en-us/windows/win32/api/profileapi/nf-profileapi-queryperformancecounter:
   

   Retrieves the current value of the performance counter, which is a high resolution (<1us) time stamp that can be used for time-interval measurements.

2. Linux: clock_gettime(): https://man7.org/linux/man-pages/man3/clock_gettime.3.html (emphasis added):
   

   CLOCK_MONOTONIC

   A nonsettable system-wide clock that represents monotonic time since—as described by POSIX—"some unspecified point in the past". On Linux, that point corresponds to the number of seconds that the system has been running since it was booted.

   CLOCK_MONOTONIC_RAW (since Linux 2.6.28; Linux-specific)

   Similar to CLOCK_MONOTONIC, but provides access to a raw hardware-based time that is not subject to NTP adjustments or the incremental adjustments performed by adjtime(3). This clock does not count time that the system is suspended.

3. Note that both clocks on both systems do NOT provide "wall clock" type timestamps. Rather, they both provide high-resolution (sub-microsecond) timestamps which generally count time since boot. These timestamps are useful for precision timing of events, producing repeatable, periodic loops, and measuring small time intervals in code, with great resolution, precision, and accuracy.

---

Update: prior to Python 3.3, the built-in Python time library (https://docs.python.org/3.5/library/time.html) didn’t have any explicitly high-resolution functions. Now, however it does provide other options, including some high-resolution functions.

My module above, however, provides high-resolution timestamps for Python code before Python 3.3, as well as after, and it does so on both Linux and Windows.

Here’s an example of what I mean, showing that the time.sleep() function is NOT necessarily a high-resolution function. On my Windows machine, it’s resolution is perhaps 8ms at best, whereas my module above has 0.5us resolution (16000 times better!) on the same machine.

Code demonstration:

import time
import GS_timing as timing

def delayMicroseconds(n):
    time.sleep(n / 1000000.)

def delayMillisecond(n):
    time.sleep(n / 1000.)

t_start = 0
t_end = 0

#using time.sleep
print('using time.sleep')
print('delayMicroseconds(1)')
for x in range(10):
    t_start = timing.micros() #us 
    delayMicroseconds(1)
    t_end = timing.micros() #us
    print('dt (us) = ' + str(t_end - t_start))
print('delayMicroseconds(2000)')
for x in range(10):
    t_start = timing.micros() #us 
    delayMicroseconds(2000)
    t_end = timing.micros() #us
    print('dt (us) = ' + str(t_end - t_start))
  
#using GS_timing
print('nusing GS_timing')
print('timing.delayMicroseconds(1)')
for x in range(10):
    t_start = timing.micros() #us 
    timing.delayMicroseconds(1)
    t_end = timing.micros() #us
    print('dt (us) = ' + str(t_end - t_start))
print('timing.delayMicroseconds(2000)')
for x in range(10):
    t_start = timing.micros() #us 
    timing.delayMicroseconds(2000)
    t_end = timing.micros() #us
    print('dt (us) = ' + str(t_end - t_start))

---

SAMPLE RESULTS ON MY WINDOWS 8.1 MACHINE (notice how much worse time.sleep does):

using time.sleep
delayMicroseconds(1)
dt (us) = 2872.059814453125
dt (us) = 886.3939208984375
dt (us) = 770.4649658203125
dt (us) = 1138.7698974609375
dt (us) = 1426.027099609375
dt (us) = 734.557861328125
dt (us) = 10617.233642578125
dt (us) = 9594.90576171875
dt (us) = 9155.299560546875
dt (us) = 9520.526611328125
delayMicroseconds(2000)
dt (us) = 8799.3056640625
dt (us) = 9609.2685546875
dt (us) = 9679.5439453125
dt (us) = 9248.145263671875
dt (us) = 9389.721923828125
dt (us) = 9637.994262695312
dt (us) = 9616.450073242188
dt (us) = 9592.853881835938
dt (us) = 9465.639892578125
dt (us) = 7650.276611328125

using GS_timing
timing.delayMicroseconds(1)
dt (us) = 53.3477783203125
dt (us) = 36.93310546875
dt (us) = 36.9329833984375
dt (us) = 34.8812255859375
dt (us) = 35.3941650390625
dt (us) = 40.010986328125
dt (us) = 38.4720458984375
dt (us) = 56.425537109375
dt (us) = 35.9072265625
dt (us) = 36.420166015625
timing.delayMicroseconds(2000)
dt (us) = 2039.526611328125
dt (us) = 2046.195068359375
dt (us) = 2033.8841552734375
dt (us) = 2037.4747314453125
dt (us) = 2032.34521484375
dt (us) = 2086.2059326171875
dt (us) = 2035.4229736328125
dt (us) = 2051.32470703125
dt (us) = 2040.03955078125
dt (us) = 2027.215576171875

---

SAMPLE RESULTS ON MY RASPBERRY PI VERSION 1 B+ (notice that the results between using time.sleep and my module are basically identical…apparently the low-level functions in time are already accessing better-resolution timers here, since it’s a Linux machine (running Raspbian)…BUT in my GS_timing module I am explicitly calling the CLOCK_MONOTONIC_RAW timer. Who knows what’s being used otherwise):

using time.sleep
delayMicroseconds(1)
dt (us) = 1022.0
dt (us) = 417.0
dt (us) = 407.0
dt (us) = 450.0
dt (us) = 2078.0
dt (us) = 393.0
dt (us) = 1297.0
dt (us) = 878.0
dt (us) = 1135.0
dt (us) = 2896.0
delayMicroseconds(2000)
dt (us) = 2746.0
dt (us) = 2568.0
dt (us) = 2512.0
dt (us) = 2423.0
dt (us) = 2454.0
dt (us) = 2608.0
dt (us) = 2518.0
dt (us) = 2569.0
dt (us) = 2548.0
dt (us) = 2496.0

using GS_timing
timing.delayMicroseconds(1)
dt (us) = 572.0
dt (us) = 673.0
dt (us) = 1084.0
dt (us) = 561.0
dt (us) = 728.0
dt (us) = 576.0
dt (us) = 556.0
dt (us) = 584.0
dt (us) = 576.0
dt (us) = 578.0
timing.delayMicroseconds(2000)
dt (us) = 2741.0
dt (us) = 2466.0
dt (us) = 2522.0
dt (us) = 2810.0
dt (us) = 2589.0
dt (us) = 2681.0
dt (us) = 2546.0
dt (us) = 3090.0
dt (us) = 2600.0
dt (us) = 2400.0

Related:

1. My 3 sets of timestamp functions (cross-linked to each other):
   1. For C timestamps, see my answer here: Get a timestamp in C in microseconds?
   2. For C++ high-resolution timestamps, see my answer here: Getting an accurate execution time in C++ (micro seconds)
   3. For Python high-resolution timestamps, see my answer here: How can I get millisecond and microsecond-resolution timestamps in Python?
2. My C and C++ Linux high-resolution timing library with millis(), micros(), nanos(), sleep_ns(), sleep_until_ns, use_realtime_scheduler(), get_estimated_resolution(), etc.
   1. timinglib.h
   2. timinglib.c
3. [my answer for C and C++, including microcontrollers (or any other system)] How to do timestamp-based, non-blocking, single-threaded cooperative multi-tasking
4. [my answer for C and C++, including microcontrollers and Arduino (or any other system)] Full coulomb counter example demonstrating the above concept with timestamp-based, single-threaded, cooperative multi-tasking
5. [my answer for C and C++ in Linux–could be easily adapted to Python using the ctypes module, as shown above] How to run a high-resolution, high-precision periodic loop in Linux easily, at any frequency (ex: up to 10 KHz~100 KHz) using a soft real-time scheduler and nanosecond delays