create missing directories for 'part-directory'

also some code improvements regarding downloader config values

docs/configuration.rst

@@ -112,7 +112,11 @@ downloader.part-directory
 =========== =====
 Type        ``string``
 Default     ``null``
-Description Path to an existing directory to store ``.part`` files in.
+Description Alternate location for ``.part`` files.
+
+            Missing directories will be created as needed.
+            If this value is ``null``, ``.part`` files are going to be stored
+            alongside the actual output files.
 =========== =====
 
 

gallery_dl/downloader/common.py

@@ -11,19 +11,29 @@
 import os
 import time
 import logging
+from .. import config, util
 
 
 class DownloaderBase():
     """Base class for downloaders"""
+    scheme = ""
     retries = 1
-    part = True
-    partdir = None
 
     def __init__(self, session, output):
         self.session = session
         self.out = output
         self.log = logging.getLogger("download")
         self.downloading = False
+        self.part = self.config("part", True)
+        self.partdir = self.config("part-directory")
+
+        if self.partdir:
+            self.partdir = util.expand_path(self.partdir)
+            os.makedirs(self.partdir, exist_ok=True)
+
+    def config(self, key, default=None):
+        """Interpolate config value for 'key'"""
+        return config.interpolate(("downloader", self.scheme, key), default)
 
     def download(self, url, pathfmt):
         """Download the resource at 'url' and write it to a file-like object"""

gallery_dl/downloader/http.py

@@ -10,23 +10,18 @@
 
 import mimetypes
 from .common import DownloaderBase
-from .. import config, util
-
-
-def _conf(key, default=None):
-    return config.interpolate(("downloader", "http", key), default)
+from .. import util
 
 
 class Downloader(DownloaderBase):
-    retries = _conf("retries", 5)
-    timeout = _conf("timeout", 30)
-    verify = _conf("verify", True)
-    part = _conf("part", True)
-    partdir = util.expand_path(_conf("part-directory"))
+    scheme = "http"
 
     def __init__(self, session, output):
         DownloaderBase.__init__(self, session, output)
         self.response = None
+        self.retries = self.config("retries", 5)
+        self.timeout = self.config("timeout", 30)
+        self.verify = self.config("verify", True)
 
     def connect(self, url, offset):
         headers = {}

gallery_dl/downloader/text.py

@@ -9,16 +9,10 @@
 """Downloader module for text: URLs"""
 
 from .common import DownloaderBase
-from .. import config, util
-
-
-def _conf(key, default=None):
-    return config.interpolate(("downloader", "text", key), default)
 
 
 class Downloader(DownloaderBase):
-    part = _conf("part", True)
-    partdir = util.expand_path(_conf("part-directory"))
+    scheme = "text"
 
     def __init__(self, session, output):
         DownloaderBase.__init__(self, session, output)