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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def write_crtf(regions, filename, coordsys='fk5', fmt='.6f', radunit='deg'):
 """ Converts a `list` of `~regions.Region` to CRTF string and write to file. Parameters regions : `list` List of `~regions.Region` objects filename : `str` Filename in which the string is to be written. Default is 'new.crtf' coordsys : `str`, optional Astropy Coordinate system that overrides the coordinate frames of all regions. Default is 'fk5'. fmt : `str`, optional A python string format defining the output precision. Default is .6f, which is accurate to 0.0036 arcseconds. radunit : `str`, optional This denotes the unit of the radius. Default is deg (degrees) Examples -------- #CRTF global coord=fk5 +circle[[1.000007deg, 2.000002deg], 5.000000deg] """


    output = crtf_objects_to_string(regions, coordsys, fmt, radunit)
    with open(filename, 'w') as fh:
        fh.write(output)