d = """{
    "motion_measure": {"INCAR": 69, "RANDOM": 63, "UNKNOWN": 62, "BIKING": 57, "WALKING": 48, "RUNNING": 41, "SEDENTARY": 0},
    "samples": [0, 1.1791444, 11.036073],
    "record_time": datetime.datetime(2018, 3, 26, 10, 3, 17, 441000)
    }"""

import ast

ast.literal_eval(d)

import json

json.loads(d)

import datetime
d = <... your string ...>
new_dict = eval(d)

import datetime
import re
import json

s = """{
    "motion_measure": {"INCAR": 69, "RANDOM": 63, "UNKNOWN": 62, "BIKING": 57, "WALKING": 48, "RUNNING": 41, "SEDENTARY": 0},
    "samples": [0, 1.1791444, 11.036073],
    "record_time": datetime.datetime(2018, 3, 26, 10, 3, 17, 441000),
    "another_time": datetime.datetime(2017, 3, 26, 10, 3, 17, 441000)
    }"""

# re.sub to replace datetime; json.loads to convert to dict
d = json.loads(re.sub(r'datetime.datetime(([^)]*))', r'"1"', s))

# datetime.datetime.strptime(...) to work with resulting datetime strings
date = datetime.datetime.strptime(d['record_time'], '%Y, %m, %d, %H, %M, %S, %f')

print(d)
# OUTPUT (shown on multiple lines for readability)
# {
# 'motion_measure': {'INCAR': 69, 'RANDOM': 63, 'UNKNOWN': 62, 'BIKING': 57, 'WALKING': 48, 'RUNNING': 41, 'SEDENTARY': 0},
# 'samples': [0, 1.1791444, 11.036073],
# 'record_time': '2018, 3, 26, 10, 3, 17, 441000',
# 'another_time': '2017, 3, 26, 10, 3, 17, 441000'
# }

print(date)
# OUTPUT
# 2018-03-26 10:03:17.441000