Alternate approach to <https://bitcoin.stackexchange.com/questions/13970/python-code-to-generate-private-ecdsa-key>.

test_ecdsaprivkey.py

#!/usr/bin/env python

from random import SystemRandom

SYS_RAN = SystemRandom()

#- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

from binascii import hexlify
from struct import Struct

PACKER = Struct('>QQQQ')
MIN_VAL = 0x1L
MAX_VAL = 0xfffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364140

def mkprivkey():
    key = SYS_RAN.randint(MIN_VAL, MAX_VAL)
    key0 = key >> 192
    key1 = (key >> 128) & 0xffffffffffffffff
    key2 = (key >> 64) & 0xffffffffffffffff
    key3 = key & 0xffffffffffffffff

    return hexlify(PACKER.pack(key0, key1, key2, key3))

#- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

HEX_CHARS = '0123456789abcdef'
MAX_HEX = 'fffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364140'

def create_private_key():
    ran_hex = ''

    for i in range(64): # pylint: disable=unused-variable
        ran_hex += HEX_CHARS[SYS_RAN.randint(0, 15)]

    return ran_hex
    # if int(ran_hex, 16) <= int(MAX_HEX, 16):
    #     return ran_hex
    # else:
    #     return create_private_key()

#- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

from binascii import unhexlify
from time import time

def timefunc(a_func, a_repetitions):
    total_s = 0

    for ignored in xrange(a_repetitions): # pylint: disable=unused-variable
        s = time()
        key = a_func()
        e = time()
        total_s += e - s

        vals = PACKER.unpack(unhexlify(key))

        val = 0
        val += vals[0] << 192
        val += vals[1] << 128
        val += vals[2] << 64
        val += vals[3]

        try:
            assert val >= MIN_VAL
            assert val <= MAX_VAL
        except AssertionError:
            print('assertion failed on: %s' % key)

    return total_s

timefunc(mkprivkey, 1000) # warm up
times = 100000
print('mkprivkey:          %0.3f ms avg' % (timefunc(mkprivkey,          times) * 1000 / times))

timefunc(create_private_key, 1000) # warm up
times = 100000
print('create_private_key: %0.3f ms avg' % (timefunc(create_private_key, times) * 1000 / times))