fixes #161

fastcore/basics.py

@@ -416,6 +416,7 @@ def argwhere(iterable, f, negate=False, **kwargs):
 # Cell
 def filter_ex(iterable, f=noop, negate=False, gen=False, **kwargs):
     "Like `filter`, but passing `kwargs` to `f`, defaulting `f` to `noop`, and adding `negate` and `gen`"
+    if f is None: f = lambda _: True
     if kwargs: f = partial(f,**kwargs)
     if negate: f = negate_func(f)
     res = filter(f, iterable)
@@ -434,9 +435,11 @@ def renumerate(iterable, start=0):
     return ((o,i) for i,o in enumerate(iterable, start=start))
 
 # Cell
-def first(x):
+def first(x, f=None, negate=False, **kwargs):
     "First element of `x`, or None if missing"
-    try: return next(iter(x))
+    x = iter(x)
+    if f: x = filter_ex(x, f=f, negate=negate, gen=True, **kwargs)
+    try: return next(x)
     except StopIteration: return None
 
 # Cell

nbs/01_basics.ipynb

@@ -2290,6 +2290,7 @@
     "#export\n",
     "def filter_ex(iterable, f=noop, negate=False, gen=False, **kwargs):\n",
     "    \"Like `filter`, but passing `kwargs` to `f`, defaulting `f` to `noop`, and adding `negate` and `gen`\"\n",
+    "    if f is None: f = lambda _: True\n",
     "    if kwargs: f = partial(f,**kwargs)\n",
     "    if negate: f = negate_func(f)\n",
     "    res = filter(f, iterable)\n",
@@ -2348,9 +2349,11 @@
    "outputs": [],
    "source": [
     "#export\n",
-    "def first(x):\n",
+    "def first(x, f=None, negate=False, **kwargs):\n",
     "    \"First element of `x`, or None if missing\"\n",
-    "    try: return next(iter(x))\n",
+    "    x = iter(x)\n",
+    "    if f: x = filter_ex(x, f=f, negate=negate, gen=True, **kwargs)\n",
+    "    try: return next(x)\n",
     "    except StopIteration: return None"
    ]
   },
@@ -2361,7 +2364,8 @@
    "outputs": [],
    "source": [
     "test_eq(first(['a', 'b', 'c', 'd', 'e']), 'a')\n",
-    "test_eq(first([]), None)"
+    "test_eq(first([False]), False)\n",
+    "test_eq(first([False], noop), None)"
    ]
   },
   {

nbs/03_xtras.ipynb

@@ -539,7 +539,7 @@
     {
      "data": {
       "text/plain": [
-       "['a', 'g', 'd', 'e', 'c', 'b', 'h', 'f']"
+       "['b', 'd', 'g', 'h', 'f', 'c', 'e', 'a']"
       ]
      },
      "execution_count": null,
@@ -940,10 +940,9 @@
    "source": [
     "def what(f):\n",
     "    with maybe_open(f, 'rb') as f:\n",
-    "        location = f.tell()\n",
-    "        h = f.read(32)\n",
+    "        location,h = f.tell(),f.read(32)\n",
     "        f.seek(location)\n",
-    "        return first(filter(None, (tf(h, f) for tf in imghdr.tests)))"
+    "        return first((tf(h,f) for tf in imghdr.tests), noop)"
    ]
   },
   {