I want to linear interpolation some points between two time string.
So I try to convert string to datetime then insert some point then convert datetime to string. but it seems the timezone not correct.
In below example. I wish to insert one point between 9-28 11:07:57.435" and "9-28 12:00:00.773".
#!/usr/bin/env python
import numpy as np
from time import mktime
from datetime import datetime
#-----------------------------------------#
def main():
dtstr = [
"9-28 11:07:57.435",
"9-28 12:00:00.773"
]
print "input",dtstr
dtlst = str2dt(dtstr)
floatlst = dt2float(dtlst)
bins = 3
x1 = list(np.arange(floatlst[0],floatlst[-1],(floatlst[-1]-floatlst[0])/bins))
dtlst = float2dt(x1)
dtstr = dt2str(dtlst)
print "output",dtstr
return
def str2dt(strlst):
dtlst = [datetime.strptime("2014-"+i, "%Y-%m-%d %H:%M:%S.%f") for i in strlst]
return dtlst
def dt2float(dtlst):
floatlst = [mktime(dt.timetuple()) for dt in dtlst]
return floatlst
def dt2str(dtlst):
dtstr = [dt.strftime("%Y-%m-%d %H:%M:%S %Z%z") for dt in dtlst]
return dtstr
def float2dt(floatlst):
dtlst = [datetime.utcfromtimestamp(seconds) for seconds in floatlst]
return dtlst
#-----------------------------------------#
if __name__ == "__main__":
main()
The output looks like:
input ['9-28 11:07:57.435', '9-28 12:00:00.773']
output ['2014-09-28 16:07:57 ', '2014-09-28 16:25:18 ', '2014-09-28 16:42:39 ']
Two questions here:
Q1. You're right about the timezones, you're using time.mktime
which converts struct_time to seconds assuming the input is local time , but then using datetime.utcfromtimestamp
which (naturally) converts to utc. Use datetime.fromtimestamp
instead to keep everything in local time.
Q2. As with the native Python range
/ xrange
, when you do numpy.arange(x, y, z)
, the result starts with x and goes upto, but not including y ( except in weird floating point roundoff cases. Don't rely on this behaviour) . if you want consistent behaviour on the end points w/ floating values, use numpy.linspace
On the other hand, why convert datetime to seconds, then go back again? datetime objects support addition and subtraction. Below would be my suggestion.
from time import mktime, localtime
from datetime import datetime
from copy import copy
def main():
input_timestrings = ["9-28 11:07:57.435", "9-28 12:00:00.773"]
input_datetimes = timestrings_to_datestimes(input_timestrings)
start_datetime = input_datetimes[0]
end_datetime = input_datetimes[1]
# subtraction between datetime objects returns a timedelta object
period_length = end_datetime - start_datetime
bins = 3
# operation w/ timedelta objects and datetime objects work pretty much as you'd expect it to
delta = period_length / bins
datetimes = list(custom_range(start_datetime, end_datetime + delta, delta))
output_timestrings = datetimes_to_timestrings(datetimes)
print output_timestrings
return
def timestrings_to_datetimes(timestrings):
datetimes = [datetime.strptime("2014-"+timestring, "%Y-%m-%d %H:%M:%S.%f") for timestring in timestrings]
return datetimes
def datetimes_to_timestrings(datetimes):
timestrings = [datetime_.strftime("%Y-%m-%d %H:%M:%S %Z%z") for datetime_ in datetimes]
return timestrings
def custom_range(start, end, jump):
x = start
while x < end:
yield x
x = x + jump
if __name__ == "__main__":
main()
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