feat(urlbuilder): customize target device pixel ratios

Author: ashutoshkrris

imgix/errors.py

@@ -27,3 +27,7 @@ class WidthToleranceError(Error):
 
 class VariableQualitiesError(Error):
     """Exception raised for an invalid variable qualities."""
+
+
+class DevicePixelRatiosError(Error):
+    """Exception raised for an invalid device pixel ratios."""

imgix/urlbuilder.py

@@ -9,6 +9,7 @@
 from base64 import urlsafe_b64encode
 from urllib.parse import quote_plus, quote
 from .validators import (
+    validate_device_pixel_ratios,
     validate_min_max_tol,
     validate_variable_qualities,
     validate_widths,
@@ -230,7 +231,7 @@ def create_srcset(self, path, params={}, options={}, **kwargs):
         options: dict, optional
             Options that will be used to generate the srcset,
             including 'disable_path_encoding', 'variable_qualities',
-            {} by default.
+            'device pixel ratios', {} by default.
         start : int, optional
             Starting minimum width value, MIN_WIDTH by default.
         stop : int, optional
@@ -335,6 +336,11 @@ def _build_srcset_DPR(
 
         qualities = {**DPR_QUALITIES, **variable_qualities}
 
+        device_pixel_ratios = options.get("device_pixel_ratios", [])
+        if device_pixel_ratios:
+            validate_device_pixel_ratios(device_pixel_ratios)
+            targets = device_pixel_ratios
+
         for dpr in targets:
             srcset_params["dpr"] = dpr
 

imgix/validators.py

@@ -1,4 +1,5 @@
 from .errors import (
+    DevicePixelRatiosError,
     VariableQualitiesError,
     WidthRangeError,
     WidthToleranceError,
@@ -208,3 +209,31 @@ def validate_variable_qualities(variable_qualities):
     """
     if not isinstance(variable_qualities, dict):
         raise VariableQualitiesError("`variable_qualities` must be a `dict`")
+
+
+def validate_device_pixel_ratios(device_pixel_ratios):
+    """Validate a list of `device_pixel_ratios`.
+
+    This function checks whether `device_pixel_ratios` is a list.
+
+
+    Parameters
+    ----------
+    device_pixel_ratios : list
+        A list of device pixel ratios.
+
+    Raises
+    ------
+    DevicePixelRatiosError
+        If `device_pixel_ratios` is not a list, raise.
+    """
+    if not isinstance(device_pixel_ratios, list):
+        raise DevicePixelRatiosError("`device_pixel_ratios` must be a `list`")
+    else:
+        all_valid_dpr = False
+        for dpr in device_pixel_ratios:
+            all_valid_dpr = isinstance(dpr, int) and dpr >= 1 and dpr <= 5
+
+        if not all_valid_dpr:
+            raise DevicePixelRatiosError("`device_pixel_ratios` can only \
+                contain positive integer values between 1 and 5")