Invert conditional, fix typo, update readme

Author: Evan Derickson

README.md

@@ -56,7 +56,7 @@ response = api.get('node["name"="Salt Lake City"]')
 
 `response` will be a dictionary representing the
 JSON output you would get [from the Overpass API
-directly](https://overpass-api.de/output_formats.html#json). 
+directly](https://overpass-api.de/output_formats.html#json).
 
 **Note that the Overpass query passed to `get()` should not contain any `out` or other meta statements.** See `verbosity` below for how to control the output.
 
@@ -98,7 +98,11 @@ response = api.get('node["name"="Salt Lake City"]', responseformat="xml")
 
 We will construct a valid Overpass QL query from the parameters you set by default. This means you don't have to include 'meta' statements like `[out:json]`, `[timeout:60]`, `[out body]`, etcetera. You just supply the meat of the query, the part that actually tells Overpass what to query for. If for whatever reason you want to override this and supply a full, valid Overpass QL query, you can set `build` to `False` to make the API not do any pre-processing.
 
-### Pre-cooked Queries: `MapQuery`, `WayQuery` 
+#### `date`
+
+You can query the data as it was on a given date. You can give either a standard ISO date alone (YYYY-MM-DD) or a full overpass date and time (YYYY-MM-DDTHH:MM:SSZ, i.e. 2020-04-28T00:00:00Z).
+
+### Pre-cooked Queries: `MapQuery`, `WayQuery`
 
 In addition to just sending your query and parse the result, `overpass`
 provides shortcuts for often used map queries. To use them, just pass

overpass/api.py

@@ -84,12 +84,12 @@ def get(self, query, responseformat="geojson", verbosity="body", build=True, dat
                           or allow the programmer to specify full query manually (False)
         :param date: a date with an optional time. Example: 2020-04-27 or 2020-04-27T00:00:00Z
         """
-        if date and not isinstance(date, datetime):
+        if date and isinstance(date, str):
             # If date is given and is not already a datetime, attempt to parse from string
             try:
                 date = datetime.fromisoformat(date)
             except ValueError:
-                # The 'Z' in a standard overpass date will through fromisoformat() off
+                # The 'Z' in a standard overpass date will throw fromisoformat() off
                 date = datetime.strptime(date, '%Y-%m-%dT%H:%M:%SZ')
         # Construct full Overpass query
         if build: