Count Strands reasoningContent, image, document, video tokens (#111 follow-up)

reasoningContent: exact counting via count_text() — pure text, no estimation
image: decode with Pillow for (w*h)/750 formula, fallback by byte size
document: ~1500 tokens/page heuristic (3KB/page of PDF)
video: ~1000 tokens/frame heuristic (30KB/frame)

Text content (reasoning, text, toolResult) uses exact tokenization.
Binary content (image, document, video) uses provider formula or
size-based estimates — accurate counting requires content extraction
that only the provider can do.

14 tests covering all Strands content block types.
This commit is contained in:
chopratejas 2026-04-08 17:31:00 -07:00
parent c92a6b9fa1
commit e7008f64d7
2 changed files with 269 additions and 0 deletions

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@ -175,6 +175,47 @@ class BaseTokenizer(ABC):
total += self._count_content_parts(tr_content)
else:
total += self.count_text(json.dumps(tr_content))
elif not part_type and "reasoningContent" in part:
# Strands SDK reasoning: {"reasoningContent": {"reasoningText": {"text": "..."}}}
# This is actual text — count it precisely.
reasoning = part["reasoningContent"]
reasoning_text = reasoning.get("reasoningText", {})
if isinstance(reasoning_text, dict):
total += self.count_text(reasoning_text.get("text", ""))
elif isinstance(reasoning_text, str):
total += self.count_text(reasoning_text)
elif not part_type and "document" in part:
# Strands SDK document: {"document": {"source": {"bytes": ...}}}
# Provider internally extracts text from PDF/DOCX then tokenizes.
# Accurate counting would require a PDF parser — instead we use
# the Anthropic documented estimate of ~1500 tokens per page,
# with ~3KB of PDF per page as a rough heuristic.
doc = part["document"]
source = doc.get("source", {})
doc_bytes = source.get("bytes", b"")
if isinstance(doc_bytes, bytes | bytearray):
estimated_pages = max(1, len(doc_bytes) // 3000)
total += estimated_pages * 1500
else:
total += self.count_text(str(doc_bytes))
elif not part_type and "image" in part:
# Strands SDK image: {"image": {"source": {"bytes": ...}}}
# Anthropic formula: tokens = (width * height) / 750.
# Decode with Pillow for exact count; fall back to estimate.
total += self._estimate_image_tokens(part["image"])
elif not part_type and "video" in part:
# Strands SDK video: provider samples ~1 fps, each frame costs
# image tokens. We can't decode frames without heavy deps, so
# estimate from byte size assuming ~30KB per frame, ~1000 tokens
# per frame (average image).
vid = part["video"]
source = vid.get("source", {})
vid_bytes = source.get("bytes", b"")
if isinstance(vid_bytes, bytes | bytearray):
frames = max(1, len(vid_bytes) // 30000)
total += frames * 1000
else:
total += 3200
else:
# Unknown type - estimate from JSON
total += self.count_text(json.dumps(part))
@ -183,6 +224,45 @@ class BaseTokenizer(ABC):
return total
@staticmethod
def _estimate_image_tokens(image_data: dict[str, Any]) -> int:
"""Estimate tokens for an image using Anthropic's formula: (w*h)/750.
Tries to decode dimensions with Pillow. Falls back to a conservative
estimate based on byte size.
"""
source = image_data.get("source", {})
img_bytes = source.get("bytes", b"")
if isinstance(img_bytes, bytes | bytearray) and len(img_bytes) > 0:
try:
import io
from PIL import Image
img = Image.open(io.BytesIO(img_bytes))
w, h = img.size
# Anthropic resizes to fit 1568x1568 max
max_dim = 1568
if w > max_dim or h > max_dim:
scale = max_dim / max(w, h)
w, h = int(w * scale), int(h * scale)
return max(100, (w * h) // 750)
except Exception:
pass
# Fallback: estimate from byte size.
# Typical screenshot: ~200KB ≈ 1200x800 ≈ 1280 tokens
if isinstance(img_bytes, bytes | bytearray):
size_kb = len(img_bytes) / 1024
if size_kb < 50:
return 400 # Small icon/thumbnail
if size_kb < 500:
return 1200 # Typical screenshot
return 1600 # Large/high-res image
return 1200 # Default estimate
def _count_tool_calls(self, tool_calls: list[dict[str, Any]]) -> int:
"""Count tokens in tool calls."""
total = 0

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@ -190,3 +190,192 @@ class TestMixedFormats:
count = t.count_messages(messages)
# Should be substantial — the tool result alone is ~700 tokens
assert count > 500, f"Mixed conversation count too low: {count}"
class TestStrandsReasoningContent:
"""Strands reasoning blocks: {"reasoningContent": {"reasoningText": {"text": "..."}}}."""
def test_reasoning_text_counted_as_text(self):
"""reasoningContent text should be counted with count_text, not estimated."""
t = _get_counter()
reasoning = "Let me think step by step about this problem. " * 100
# Strands format
msg_strands = [
{
"role": "assistant",
"content": [{"reasoningContent": {"reasoningText": {"text": reasoning}}}],
}
]
# Equivalent plain text for comparison
msg_plain = [{"role": "assistant", "content": reasoning}]
s = t.count_messages(msg_strands)
p = t.count_messages(msg_plain)
assert s == p, f"Reasoning={s} should equal plain text={p}"
def test_reasoning_plus_text_both_counted(self):
"""Message with both reasoning and text blocks."""
t = _get_counter()
msg = [
{
"role": "assistant",
"content": [
{"reasoningContent": {"reasoningText": {"text": "thinking " * 200}}},
{"text": "Here is my answer " * 50},
],
}
]
count = t.count_messages(msg)
# Should be substantial — both blocks counted
assert count > 200, f"Combined reasoning+text too low: {count}"
class TestStrandsMediaContent:
"""Strands image, document, video blocks."""
def test_image_not_zero(self):
"""Image block should have nonzero token count."""
t = _get_counter()
msg = [
{
"role": "user",
"content": [{"image": {"format": "png", "source": {"bytes": b"x" * 50000}}}],
}
]
count = t.count_messages(msg)
assert count > 100, f"Image count too low: {count}"
def test_document_not_zero(self):
"""Document block should have nonzero token count."""
t = _get_counter()
msg = [
{
"role": "user",
"content": [
{
"document": {
"format": "pdf",
"name": "report.pdf",
"source": {"bytes": b"x" * 30000},
}
}
],
}
]
count = t.count_messages(msg)
assert count > 1000, f"Document count too low: {count}"
def test_video_not_zero(self):
"""Video block should have nonzero token count."""
t = _get_counter()
msg = [
{
"role": "user",
"content": [{"video": {"format": "mp4", "source": {"bytes": b"x" * 300000}}}],
}
]
count = t.count_messages(msg)
assert count > 1000, f"Video count too low: {count}"
class TestStrandsFullConversation:
"""End-to-end conversation with all Strands content types."""
def test_agent_conversation_with_reasoning_and_tools(self):
"""Realistic Strands agent conversation."""
t = _get_counter()
messages = [
{"role": "user", "content": [{"text": "Analyze this code and fix the bug"}]},
{
"role": "assistant",
"content": [
{
"reasoningContent": {
"reasoningText": {"text": "Let me examine the code carefully. " * 50}
}
},
{
"toolUse": {
"toolUseId": "t1",
"name": "read_file",
"input": {"path": "main.py"},
}
},
],
},
{
"role": "user",
"content": [
{
"toolResult": {
"toolUseId": "t1",
"content": [
{
"text": "def process():\n data = fetch()\n return transform(data)\n"
* 50
}
],
}
},
],
},
{
"role": "assistant",
"content": [
{
"reasoningContent": {
"reasoningText": {"text": "The bug is in the transform function. " * 30}
}
},
{"text": "I found the issue. The transform function doesn't handle None."},
],
},
]
count = t.count_messages(messages)
# Reasoning + tool result + text = should be substantial
assert count > 500, f"Full conversation too low: {count}"
# Verify reasoning contributes meaningfully
no_reasoning = [
{"role": "user", "content": [{"text": "Analyze this code"}]},
{
"role": "assistant",
"content": [
{
"toolUse": {
"toolUseId": "t1",
"name": "read_file",
"input": {"path": "main.py"},
}
},
],
},
{
"role": "user",
"content": [
{
"toolResult": {
"toolUseId": "t1",
"content": [
{
"text": "def process():\n data = fetch()\n return transform(data)\n"
* 50
}
],
}
},
],
},
{
"role": "assistant",
"content": [
{"text": "I found the issue."},
],
},
]
count_no_reasoning = t.count_messages(no_reasoning)
assert count > count_no_reasoning + 100, (
f"Reasoning should add significant tokens: with={count}, without={count_no_reasoning}"
)