Examples: Manipulating Headers

Example 1: Change the data time in the fixed header to 12:00 01/02/03

import mule

ff = mule.FieldsFile.from_file("InputFile")

ff.fixed_length_header.t1_year = 2003
ff.fixed_length_header.t1_month = 2
ff.fixed_length_header.t1_day = 1
ff.fixed_length_header.t1_hour = 12
ff.fixed_length_header.t1_minute = 0

ff.to_file("OutputFile")

Note

• You could instead choose to refer to the indices of the raw array (e.g. ff.fixed_length_header.raw[21] = 2003, etc.) though the form above is preferable (more readable).

Example 2: Change the forecast time (lbft) in the 3rd lookup header to 12

import mule

ff = mule.FieldsFile.from_file("InputFile")
ff.fields[2].lbft = 12
ff.to_file("OutputFile")

Note

• You could instead choose to refer to the indices of the raw array (e.g. ff.fields[2].raw[14] = 12) though the named form is preferable (more readable).

• In this example we are assuming that the 2nd field in the file has a valid header release number (lbrel == 2 or 3); if it didn’t then it may not have an lbft attribute.

Example 3: Change the validity time in all lookup headers to 12:00 01/02/03

import mule

ff = mule.FieldsFile.from_file("InputFile")

for field in ff.fields:
    if field.lbrel in (2,3):
        field.lbyr = 2003
        field.lbmon = 2
        field.lbdat = 1
        field.lbhr = 12
        field.lbmin = 0

ff.to_file("OutputFile")

Note

• You could instead choose to refer to the indices of the raw array (e.g. field.raw[1] = 2003) though the named form is preferable (more readable).

• Notice the check on lbrel - only fields with a valid release number will correctly support all named lookup attributes (lbyr, lbmon, etc.) so ignore other field types to avoid problems (good practice).

Example 4: Round the validity time in all lookup headers to the nearest hour

import mule
from datetime import datetime, timedelta

ff = mule.FieldsFile.from_file("InputFile")

for field in ff.fields:
    if field.lbrel in (2,3):
        # Create a datetime object (handles date incrementing logic)
        field_date = datetime(
            field.lbyr, field.lbmon, field.lbdat, field.lbhr, field.lbmin)
        # Create and apply a timedelta to take the time to the nearest hour
        if field_date.minute >= 30:
            incr_seconds = (60 - field_date.minute)*60
            field_date += timedelta(seconds=incr_seconds)
        else:
            incr_seconds = field_date.minute*60
            field_date -= timedelta(seconds=incr_seconds)
        # Now extract the components again to set the lookup values
        field.lbyr = field_date.year
        field.lbmon = field_date.month
        field.lbdat = field_date.day
        field.lbhr = field_date.hour
        field.lbmin = field_date.minute

ff.to_file("OutputFile")

Note

• You could instead choose to refer to the indices of the raw array (e.g. field.raw[1] = field_date.year) though the named form is preferable (more readable).

• Notice the check on lbrel - only fields with a valid release number will correctly support all named lookup attributes (lbyr, lbmon, etc.) so ignore other field types to avoid problems (good practice).

• This example uses the Python datetime library, which should be treated with some caution (its timezone support is not particularly robust) - a possible alternative would be the isodatetime module.

Example 5: Change the data time in all lookup headers to 12:00 01/02/03 and reset forecast hour to match

import mule
from datetime import datetime, timedelta

ff = mule.FieldsFile.from_file("InputFile")

# Create a datetime object at the reference time
field_data_t_new = datetime(2003, 2, 1, 12, 0)

for field in ff.fields:
    if field.lbrel in (2,3):
        # Create a datetime object (handles date incrementing logic)
        field_data_t = datetime(
            field.lbyrd, field.lbmond, field.lbdatd, field.lbhrd, field.lbmind)
        # The datetime objects will return a timedelta object when subtracted
        data_t_delta = field_data_t_new - field_data_t
        # Convert this delta to whole hours (truncated)
        data_t_delta_hours = data_t_delta.days*24.0 + data_t_delta.seconds//3600
        # Set the lookup values
        field.lbyrd = field_data_t_new.year
        field.lbmond = field_data_t_new.month
        field.lbdatd = field_data_t_new.day
        field.lbhrd = field_data_t_new.hour
        field.lbmind = field_data_t_new.minute
        # Adjust the forecast time by the amount calculated above
        field.lbft += data_t_delta_hours

ff.to_file("OutputFile")

Note

• You could instead choose to refer to the indices of the raw array (e.g. fields.raw[1] = field_date.year) though the named form is preferable (more readable).

• Notice the check on lbrel - only fields with a valid release number will correctly support all named lookup attributes (lbyrd, lbmond, etc.) so ignore other field types to avoid problems (good practice).

• This example uses the Python datetime library, which should be treated with some caution (its timezone support is not particularly robust) - a possible alternative would be the isodatetime module.