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How can I simplify the function to find out if a string contains coordinates that describe a polygon?

I have the following line:

points = "34.09352 -118.27483, 34.0914 -118.2758, 34.082 -118.2782, 34.0937 -118.2769, 34.0933 -118.2748"

points

is a string containing coordinate values ​​(latitude and longitude), separated by commas.

I want to check that this string only contains integers or float values ​​and the first coordinate is equal to the last one.

I have the following code for this:

def validate_points(points):
   coordinates = points.split(',')

   for point in coordinates:
      latlon = point.split(' ')

      latitude = latlon[0]
      longitude = latlon[1]
      if not is_number(latitude) or not is_number(longitude):
         raise WrongRequestDataError("Please, specify the correct type of points value. It must be a numeric value")

   first = coordinates[0]
   last = coordinates[len(coordinates) - 1]
   if first != last:
        raise WrongRequestDataError("Incorrect points format, the first point must be equal to last")

def is_number(s):
   try:
     if float(s) or int(s):
        return True
   except ValueError:
        return False

Is there a way to simplify or speed up this code?

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5 answers


Your entrance almost looks like a WKT polygon .

Using the package shapely

, you can simply try to parse the points as WKT and see what happens, according to Python's "It's easier to ask for forgiveness than permission" :



# pip install shapely
from shapely import wkt

def is_well_defined_polygon(points):
    try:
        wkt.loads("POLYGON((%s))" % points)
        return True
    except:
        return False

points = "34.09352 -118.27483, 34.0914 -118.2758, 34.082 -118.2782, 34.0937 -118.2769, 34.0933 -118.2748, 34.09352 -118.27483"

print(is_well_defined_polygon(points))
# True
print(is_well_defined_polygon("1 2, 3 4"))
# IllegalArgumentException: Points of LinearRing do not form a closed linestring
# False
print(is_well_defined_polygon("a b c d"))
# ParseException: Expected number but encountered word: 'a'
# False
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Here are some improvements. You can speed up the is_number function a little and use coordinates[-1]

[len (coordinates) -1] instead of `coordinates. You also don't have to define all of these variables:



def validate_points(points):
   coordinates = points.split(',')

   for point in coordinates:
       latitude, longitude = point.split(' ', 1)

       if not is_number(latitude) or not is_number(longitude):
          raise WrongRequestDataError("Please, specify the correct type of points value. It must be a numeric value")

   if coordinates[0] != coordinates[- 1]:
       raise WrongRequestDataError("Incorrect points format, the first point must be equal to last")
def is_number(s):
   try:
        return (float(s) or int(s) or True)
   except ValueError:
       return False
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Minor things:

  • Use coordinates[-1]

    insteadcoordinates[len(coordinates)-1]

  • Use latitude, longitude = point.split(' ', 1)

    . This will invalidate cases like 3.41 47.11 foobar

    .
  • Do you really need latitude

    and longitude

    for lines? You probably want a float / int value, so it is_number

    should be something like
    def conv_number (s):
    try:
        return float (s)
    except ValueError:
        try:
            return int (s)
        except ValueError:
            raise WrongRequestDataError (s)

I especially like that you don't use isinstance

float / int for validation: in python you should always be able to pass in an arbitrary object that acts like int

or float

if asked to do so.

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This is how I would do it:

points = "34.09352 -118.27483, 34.0914 -118.2758, 34.082 -118.2782, 34.0937 -118.2769, 34.0933 -118.2748"


def validate_points(points):
    separate = points.split(',')

    try:
        [float(y) for x in separate for y in x.split()]
    except ValueError:
        return False

    return separate[0] == separate[-1]

print(validate_points(points))  # False

If you really want to raise a bug, you can change / simplify the code like this:

def validate_points(points):
    separate = points.split(',')
    [float(y) for x in separate for y in x.split()]  # orphan list-comprehension
    if not separate[0] == separate[-1]:
        raise ValueError
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my solution using Regex named group to filter data:

# -*- coding: utf-8 -*-
import re


class WrongRequestDataError(Exception):
    pass

def position_equal(pos1, pos2):
    # retrun pos1 == pos2 # simple compare
    accuracy = 0.005
    return (
        abs(float(pos1['latitude']) - float(pos2['latitude'])) <= accuracy and
        abs(float(pos1['longitude']) - float(pos2['longitude'])) <= accuracy
    )

test_str = "34.09352 -118.27483, 34.0914 -118.2758, 34.082 -118.2782, 34.0937 -118.2769, 34.0933 -118.2748"

regex = r"(?P<position>(?P<latitude>\-?\d+(\.\d+)?) (?P<longitude>\-?\d+(\.\d+)?))"
matches = re.finditer(regex, test_str, re.IGNORECASE)

matched = []
for matchNum, match in enumerate(matches):
    matched.append({
        'latitude': match.group('latitude'),
        'longitude': match.group('longitude'),
    })

matched_count = len(matched)
if matched_count != test_str.count(',') + 1:
    raise WrongRequestDataError("Please, specify the correct type of points value. It must be a numeric value")
else:
    if matched_count > 1:
        if not position_equal(matched[0], matched[-1]):
            raise WrongRequestDataError("Incorrect points format, the first point must be equal to last")

You can change the precision value in the position_equal function to change the precision when comparing the first and last position.

You can check or debug regex in regex101: https://regex101.com/r/tYYJXN/1/

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