Change sleep interval between requests

These are now adapted to how many requests have already been done. With
the current settings, Instaloader does not more than

12 request in the first ten seconds,
28 requests in the first minute,
40 requests in the first two minutes,
63 requests in the first five minutes,
90 requests in the first ten minutes,
and after that 50 requests per ten minutes.

This should make it less likely that Instaloader is rate-limited by
Instagram, while still being fast if downloading only a few posts.

Further, option --no-sleep is hidden in --help output and README.rst.

README.rst

@@ -222,8 +222,6 @@ How to Download
                            Defaults to ``{date:%Y-%m-%d_%H-%M-%S}``.
 --user-agent USER_AGENT    User Agent to use for HTTP requests. Per default,
                            Instaloader pretends being Chrome/51.
---no-sleep                 Do not sleep between requests to Instagram's servers.
-                           This makes downloading faster, but may be suspicious.
 
 Miscellaneous Options
 ^^^^^^^^^^^^^^^^^^^^^

instaloader.py

@@ -15,7 +15,7 @@ import sys
 import tempfile
 import time
 import urllib.parse
-from argparse import ArgumentParser
+from argparse import ArgumentParser, SUPPRESS
 from base64 import b64decode, b64encode
 from contextlib import contextmanager, suppress
 from datetime import datetime
@@ -364,6 +364,10 @@ class Instaloader:
         # error log, filled with error() and printed at the end of Instaloader.main()
         self.error_log = []
 
+        # For the adaption of sleep intervals (rate control)
+        self.request_count = 0
+        self.last_request_time = 0
+
     @property
     def is_logged_in(self) -> bool:
         return bool(self.username)
@@ -375,8 +379,12 @@ class Instaloader:
                                  self.dirname_pattern, self.filename_pattern,
                                  self.download_videos, self.download_geotags,
                                  self.download_captions, self.download_comments)
+        new_loader.request_count = self.request_count
+        new_loader.last_request_time = self.last_request_time
         yield new_loader
         self.error_log.extend(new_loader.error_log)
+        self.request_count = new_loader.request_count
+        self.last_request_time = new_loader.last_request_time
 
     def _log(self, *msg, sep='', end='\n', flush=False):
         """Log a message to stdout that can be suppressed with --quiet."""
@@ -403,9 +411,18 @@ class Instaloader:
                 self.error('{}'.format(err))
 
     def _sleep(self):
-        """Sleep a short, random time if self.sleep is set. Called before each request to the instagram.com."""
+        """Sleep a short time if self.sleep is set. Called before each request to instagram.com."""
-        if self.sleep:
+        if not self.sleep:
-            time.sleep(random.uniform(0.5, 1.75))
+            return
+        max_sleep_int = 600/50     # 50 requests per 10 minutes
+        count_for_max_sleep  = 80  # after 80 requests.
+        sleep_interval = min(self.request_count, count_for_max_sleep) / count_for_max_sleep * max_sleep_int
+        current_time = time.monotonic()
+        sleep_time = self.last_request_time + sleep_interval - current_time
+        if sleep_time > 0.0:
+            time.sleep(sleep_time)
+        self.request_count += 1
+        self.last_request_time = max(current_time, self.last_request_time + sleep_interval)
 
     def _get_and_write_raw(self, url: str, filename: str, tries: int = 3) -> None:
         """Downloads raw data.
@@ -1342,9 +1359,7 @@ def main():
                             '\'{date:%%Y-%%m-%%d_%%H-%%M-%%S}\'.')
     g_how.add_argument('--user-agent',
                        help='User Agent to use for HTTP requests. Defaults to \'{}\'.'.format(default_user_agent()))
-    g_how.add_argument('-S', '--no-sleep', action='store_true',
+    g_how.add_argument('-S', '--no-sleep', action='store_true', help=SUPPRESS)
-                       help='Do not sleep between requests to Instagram\'s servers. This makes downloading faster, but '
-                            'may be suspicious.')
 
     g_misc = parser.add_argument_group('Miscellaneous Options')
     g_misc.add_argument('-O', '--shorter-output', action='store_true',