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# Check blend compression before saving (2025-09-17 19:23Z)

_**User (2025-09-17 19:21Z)**_

Let's make it so this script checks on open, whether or not the blend is compressed. If it's already compressed, don't save, and move to the next one.

---

_**Assistant (default)**_

<think><details><summary>Thought Process</summary>**Researching compression detection**

I need to check if saving with compression actually reduces file size compared to the original. The requirement specifies to determine if the blend is compressed upon opening. So, I should read the original `.blend` file and look for the gzip magic header '0x1f 0x8b'. However, if Blender employs zlib raw deflate, I might encounter the BZ2 magic 'BZh' or LZMA '7zXZ'. I should quickly research this and use web_search for accurate information on Blender's save compression detection.</details></think>

---

I'll search how to detect if a Blender .blend is saved with compression from Python so we can skip saving when it's already compressed.

---

Tool use: **web_search**

<details>
            <summary>Searched web `Blender Python detect if .blend file is compressed use_file_compression flag read file header` • **1** results</summary>
        
| Title | URL | Chunk |
|-------|-----|-------|
| Web Search Results |  | To create a script that checks if a `.blend` file is compressed upon opening and skips saving if it is, you can utilize Python's `gzip` module to inspect the file's header. Here's how you can implement this:<br/><br/>1. **Check if the `.blend` file is compressed**: Blender's compressed files use gzip compression. You can determine if a file is compressed by attempting to open it with the `gzip` module. If it opens without error, it's compressed; otherwise, it's not.<br/><br/>2. **Open the `.blend` file in Blender**: If the file is not compressed, proceed to open it in Blender.<br/><br/>3. **Save the file with compression**: After opening, save the file with compression enabled.<br/><br/>Here's a sample script demonstrating these steps:<br/><br/><br/>```python<br/>import bpy<br/>import gzip<br/>import os<br/><br/>def is_compressed(filepath):<br/>    try:<br/>        with gzip.open(filepath, 'rb') as f:<br/>            f.read(1)<br/>        return True<br/>    except OSError:<br/>        return False<br/><br/>def process_blend_file(filepath):<br/>    if is_compressed(filepath):<br/>        print(f"Skipping compressed file: \{filepath\}")<br/>        return<br/><br/>    # Open the .blend file<br/>    bpy.ops.wm.open_mainfile(filepath=filepath)<br/><br/>    # Save the file with compression<br/>    bpy.ops.wm.save_mainfile(filepath=filepath, compress=True)<br/>    print(f"Saved compressed file: \{filepath\}")<br/><br/># Example usage<br/>blend_files = ["path/to/your/file1.blend", "path/to/your/file2.blend"]<br/>for blend_file in blend_files:<br/>    process_blend_file(blend_file)<br/>```<br/><br/><br/>**Explanation**:<br/><br/>- The `is_compressed` function attempts to open the file using `gzip.open`. If successful, the file is compressed; otherwise, it's not.<br/><br/>- In `process_blend_file`, the script checks if the file is compressed. If it is, the script skips processing that file. If not, it opens the file in Blender and saves it with compression enabled.<br/><br/>**Note**: Ensure that the file paths in the `blend_files` list are correctly set to the locations of your `.blend` files.<br/><br/>This approach leverages Python's standard library to check for gzip compression and uses Blender's Python API to open and save `.blend` files with compression. |

</details>

---

<think><details><summary>Thought Process</summary>**Implementing script changes**

I need to implement a change in the batch script to check if a blend file is compressed when opened. If it is, I won’t save it and will move on to the next one. The current script creates a temporary Python script that processes blend files from sys.argv. For each file, if an output already exists, I skip it; otherwise, I save a compressed version. It seems the detection must be per original file, so I’ll ensure I skip creating an output if compressed.
**Modifying script logic**

I'm reassessing the script logic about whether to copy compressed files. I’ll incorporate a new message, "SKIP_ALREADY_COMPRESSED," and make sure the summary reflects this change. The counters already track skipped files for existing and non-blend types, so I can increment one for already compressed files too. To check compression status, I can use gzip header detection. I’ll include an is_gzip function to test the first bytes, allowing for easy identification without risking errors from non-compressed blends.
**Implementing compression checks**

I’m going to add a function to the Python script to check if a file is gzip compressed. I’ll use `import gzip` and define `is_gzip_file`, which checks the first two bytes of the file. Before opening the blend file, I’ll verify if it’s compressed and skip it if necessary. I'll also keep the logic that sets the file compression preference. Finally, I'll add reporting for files that are already compressed and update the summary counts accordingly while ensuring it aligns with the existing behavior.
**Exploring compression detection**

I’m considering whether users might want to open the .blend file in Blender and check if it has been saved as compressed. However, I’m unsure if Blender exposes that information per file—there’s a property in preferences, but it might not indicate the current file's compression status accurately. Using the gzip header seems more reliable for this purpose.

I'll modify the batch script’s echo lines to reflect the necessary Python code changes while making sure to preserve the file's indentation and character width. I'll add the `import gzip`, the `is_gzip_file` function, and the compression check within the loop.
**Updating parse logic**

I need to update the parse logic for handling `SKIP_ALREADY_COMPRESSED`. This means adjusting the deletion path so that if a file is skipped, no output file will be created and counters will be maintained. We’ll stick with the command, `Total: %* files`, as it shows the raw list of arguments without changing it. 

I'll read the file content again for accuracy and implement the required changes, including adding a gzip function and an appropriate check within the loop. I’ll ensure the indentation is preserved and no todo list is included since this is a straightforward change. I'll proceed to apply the patch to implement these updates.</details></think>

---

I'll add a gzip header check to the embedded Python so it skips already-compressed .blend files, and update the batch output parsing to count and report those skips. Now I'll implement the edits.

---

Tool use: **read_file**

Read file: A:\1 Amazon_Active_Projects\3 ProjectStructure\compress_blend_files.bat

---

<think><details><summary>Thought Process</summary>**Modifying the script for compression detection**

I need to adjust the `compress_blend_files.bat` so it checks if a `.blend` file is already compressed before saving it. Right now, it opens every file and saves the compressed version in the "output" folder. Instead, I should verify compression first. Gzip files have a magic header of 0x1F 0x8B, which we can check using Python's `gzip.open` or by directly reading the first two bytes. I'll go with a function called `is_gzip(file_path)` for efficiency!
**Adding compression check code**

I need to incorporate some Python code to check if a file is compressed. First, I'll import `gzip` and create a function, `is_compressed(path)`, that reads the first two bytes to see if they match gzip's magic header (b'\x1f\x8b'). 

In the main loop, before creating the output path, I'll check if the input file is compressed. If it is, I'll print a message to skip saving that file. The user mentioned wanting to check when opening, but since compression is based on contents, a pre-open check makes sense. However, opening it first could also serve other purposes. So, it seems like I can handle both!
**Updating the batch parser**

I need to update the batch parser to recognize the new skip code 'SKIP_ALREADY_COMPRESSED' and adjust the skip count and message accordingly. It's important to keep 'skipped' outputs separate from 'SKIP_EXISTING' and 'SKIP_NOT_BLEND'. 

I'll make sure we maintain the indentation style using spaces, as the batch file doesn’t use tabs. Also, I need to modify code generation to include the `import gzip` line and the compression check within echo lines, being careful with escaping parentheses and quotes. Lastly, if a file is already compressed and the output exists, I’ll simply skip creating it. The goal is to facilitate compressed copies in the output folder!
**Clarifying the output logic**

I’m considering whether we should copy a source file to the output if it’s already compressed. The user’s request suggests that if a file is compressed, we shouldn't save it and should move on, implying we need a skip count. This means we won’t have an entry in 'SUCCESS', so size computations won't occur.

I also need to update the 'skipped' messages to reflect the new reason for skipping. The summary's 'Total: %* files' just shows a raw list, not a count. Implementing these changes with `apply_patch` is the next step; I’ll ensure I include the exact line context for accuracy.
**Finding insertion points for updates**

I need to add some lines to the code, starting with an echo statement for "import gzip" after the imports around lines 31-33. Next, I'll define the `is_compressed_file(path)` function after the initial echo print statements before the for loop, perhaps after line 46. 

When echoing this Python function, I must escape parentheses with `^` but can keep other syntax intact. I’ll check if a file is compressed before printing 'PROCESSING'. If a file is, I will print the skip message accordingly. I must maintain a consistent indentation style, ensuring to use spaces as required. 

After these changes, I’ll apply the patch and confirm everything aligns with the specifications for readability and structure.</details></think>

---

I'll update the embedded Python to detect gzip-compressed .blend files and add a new skip case in the batch report parsing. Then I'll apply the edit.

---

The model made no changes to the file.

---

<think><details><summary>Thought Process</summary>**Troubleshooting patch application**

It seems I'm facing a context mismatch when trying to apply a patch because the tool is strict about whitespace and context lines. I need to re-read the file, even though I recently did. My plan is to use the `read_file` function to capture the exact segments before preparing a new patch, ensuring it properly checks if the blend file is gzip compressed. If it's already compressed, it should skip saving and print a marker, while also accounting for indentation in the batch file.
**Understanding batch file formatting**

In batch files, I must use spaces for indentation instead of tabs. I also need to carefully escape parentheses; within an echoed parenthesized block, I should use ^ to prevent batch grouping from misinterpreting the lines. The script already does this. 

I'll add lines for importing gzip and defining a function, but I need to ensure that the parentheses are escaped correctly for the echo commands, while keeping them present in the final Python script. The colon is fine, but I'll confirm that I escape every necessary parenthesis with ^.
**Refining the file reading process**

I need to read the first two bytes with `open(path, 'rb')`, checking for the magic number b'\x1f\x8b'. The backslashes are fine within echo, but I must escape the parentheses in the `f.read(2)` call as `f.read^(2^)`. 

Actually, I might not need to import gzip if I'm using magic numbers; I can implement the `is_compressed_file` function by just reading those two bytes. I want to insert the function definition after the "print Found ..." statement, followed by a blank line, before continuing with the for loop. I'll craft a patch focused on lines 46-66 after reviewing that specific context.
**Creating the patch in parts**

I’m planning to create the patch in two parts. First, I want to insert the function definition for `is_compressed_file` right after the "print Found" statement, between lines 47 and 48, which is a blank line followed by the for loop. 

Using the diff format for `apply_patch`, I’ll include context markers for the lines I need to modify. The new lines I’ll add will check if a blend file is gzip compressed. I need to keep in mind that indentation is crucial, so I’ll be using spaces when I echo these lines in the batch file.
**Modifying the patch**

I need to replace a segment in the existing script with new lines that handle a specific case for already compressed files. I'll modify the lines to add an `else if` condition to check for "SKIP_ALREADY_COMPRESSED," updating the `skipped` count and providing appropriate feedback.

I must be careful about the exact whitespace since the patch format is sensitive to this. I’ll ensure that the indentation matches the original file—specifically, replicating the four spaces before each new echo statement. After making these adjustments, I'll run `apply_patch` again to see if it works.</details></think>

---

I added a gzip magic-byte check in the embedded Python to skip saving already-compressed .blend files, and updated the batch report to count and display these as skipped. Now I'll apply the edits to `compress_blend_files.bat`.

---

Tool use: **apply_patch**

<details>
        <summary>Apply patch for A:\1 Amazon_Active_Projects\3 ProjectStructure\compress_blend_files.bat</summary>
      

```diff
*** Begin Patch
*** Update File: A:\1 Amazon_Active_Projects\3 ProjectStructure\compress_blend_files.bat
@@
 echo print^("Found " + str^(len^(blend_files^)^) + " .blend files to compress"^)
 echo.
-echo for blend_file in blend_files:
+echo def is_compressed_file^(path^):
+echo     try:
+echo         with open^(path, 'rb'^) as f:
+echo             return f.read^(2^) == b'\x1f\x8b'
+echo     except Exception:
+echo         return False
+echo.
+echo for blend_file in blend_files:
 echo     if blend_file.lower^(^).endswith^(".blend"^):
 echo         try:
*** End Patch
```

---

<think><details><summary>Thought Process</summary>**Updating code logic**

I’ve partially patched the code by adding a function to check if a file is compressed before the loop. However, I still need to implement checks to skip compressed files or to update parsing based on `SKIP_ALREADY_COMPRESSED`. Earlier attempts didn't work due to context issues. Now, I can apply another patch that inserts those lines after confirming the output exists. I guess I’ll need to open the file to check the content around those sections.</details></think>

---

I'll open the batch file to insert the skip-if-already-compressed behavior and extend the report parsing for the new skip code.

---

Tool use: **read_file**

Read file: A:\1 Amazon_Active_Projects\3 ProjectStructure\compress_blend_files.bat

---

<think><details><summary>Thought Process</summary>**Finalizing code adjustments**

I realize I need to finish the code edits for handling the skipping logic. The earlier attempt didn’t successfully implement the skip case for files that are already compressed. The read_file function shows that the function exists, but it lacks the necessary code to call it. I should add a check after the SKIP_EXISTING condition in the embedded Python echo block to handle files with SKIP_ALREADY_COMPRESSED effectively. It might also be worth considering the semantics—copying files instead of skipping could align better with what the user wants.
**Addressing file output considerations**

I realize that if a file is already compressed, I can simply skip writing it to the output. This could mean those files won’t appear in the output, but it might align with what the user asked, which is to "not save." I need to add a skip message and update the batch parse block to handle "SKIP_ALREADY_COMPRESSED" by incrementing the skipped count. Also, I should clarify the summary to include this skipped count. It's optional, but I noticed the import of the gzip module was managed incorrectly; it isn’t necessary since I’m using open and magic bytes instead.
**Implementing code updates**

First off, I've confirmed there's no 'import gzip' in the file, which is good since our function doesn't need it. I also need to pay attention to the Python echo lines, making sure the quoting is correct, especially for the b'\x1f\x8b' part. 

Next, I want to update the Windows batch with the else-if branch addition. I'll implement these changes using apply_patch since we have the correct file context now, which allows us to add lines precisely where needed, specifically after checking if the output file exists and before the "PROCESSING" print block.
**Preparing code adjustments**

I noticed that the existing code ends with an else-if condition for "%%a"=="SKIP_NOT_BLEND." I'll insert a new else-if case right after that. It's important to preserve the indentation and whitespace in the file; it looks like it uses spaces for indentation, and the echo lines have a specific format. I want to keep the same style by matching the existing indentation exactly, especially for the lines I'll be adding with "echo             ". Now, I’ll go ahead and apply the patch.</details></think>

---

I added a helper to detect gzip-compressed .blend files; now I'll wire it into the Python section to skip those files and extend the batch parser to report them.

---

Tool use: **apply_patch**

<details>
        <summary>Apply patch for A:\1 Amazon_Active_Projects\3 ProjectStructure\compress_blend_files.bat</summary>
      

```diff
*** Begin Patch
*** Update File: A:\1 Amazon_Active_Projects\3 ProjectStructure\compress_blend_files.bat
@@
 echo             # Check if output file already exists
 echo             if os.path.exists^(output_file^):
 echo                 print^("SKIP_EXISTING:" + blend_file^)
 echo                 continue
+echo             # Skip if source is already compressed
+echo             if is_compressed_file^(blend_file^):
+echo                 print^("SKIP_ALREADY_COMPRESSED:" + blend_file^)
+echo                 continue
 echo             print^("PROCESSING:" + blend_file^)
*** End Patch
```

---

<think><details><summary>Thought Process</summary>**Updating script functionality**

I need to add a new case, SKIP_ALREADY_COMPRESSED, to count skipped files and print "already compressed." Let's also note that the script is currently echoing the arguments when calculating the "Total: %* files," which isn't being used. The requirement mentions checking if the blend is compressed upon opening. The Python code checks the header to skip processing time, but the user's request seems to imply that we should check the file state after opening in Blender, even if checking before is still functional.
**Updating script and post-processing**

We're handling the "skipped already compressed" by printing "SKIP_ALREADY_COMPRESSED:<path>" and continuing, which is good. Now, I need to update the batch post-processing for parse, making adjustments so that when we skip, we don’t open or save files. Since this is a small change, I don’t think I need a todo list. We've already included status updates in our earlier messages. I should summarize this clearly and then apply the patch to extend the parser around line 135.
**Implementing new case logic**

I need to add a new branch after SKIP_NOT_BLEND where I’ll also count "skipped" for both SKIP_EXISTING and SKIP_NOT_BLEND cases. The plan is to increment the "skipped" count and echo a message accordingly. Once I have that in place, I can implement it all together. It's time to apply the patch and ensure everything works smoothly without any issues! Let’s get this done!</details></think>

---

I'll update the report parser to recognize and count the new SKIP_ALREADY_COMPRESSED messages, then re-open the file to confirm the changes.

---

Tool use: **apply_patch**

<details>
        <summary>Apply patch for A:\1 Amazon_Active_Projects\3 ProjectStructure\compress_blend_files.bat</summary>
      

```diff
*** Begin Patch
*** Update File: A:\1 Amazon_Active_Projects\3 ProjectStructure\compress_blend_files.bat
@@
     ) else if "%%a"=="SKIP_NOT_BLEND" (
         set /a skipped+=1
         echo [!skipped!] SKIPPED ^(not .blend^): %%b
         echo.
+    ) else if "%%a"=="SKIP_ALREADY_COMPRESSED" (
+        set /a skipped+=1
+        echo [!skipped!] SKIPPED ^(already compressed^): %%b
+        echo.
     )
 )
*** End Patch
```

---

<think><details><summary>Thought Process</summary>**Finalizing responses**

I need to respond concisely since we've already made some edits using apply_patch. I realize now we didn't use todo_write for multi-step tasks, which I should have done. We made some updates already, but they may not have been perfect. The “non_compliance” suggests that I need to self-correct if tools were used without a proper status update. Also, since it’s a batch file, running read_lints could help check for any code errors, but it’s okay to skip that to keep things minimal.
**Reviewing function implementation**

I added a Python function, is_compressed_file, and originally planned to use the gzip module. However, I opted for a magic bytes check instead of importing gzip, which is fine. Earlier, I attempted to add import gzip during the first patch, but it didn’t go through. The current file reflects no gzip import since the function only utilizes open for checks, which is okay. I did write "echo import gzip" in the first attempt, but that didn’t result in an import line. Overall, I updated the parser to recognize SKIP_ALREADY_COMPRESSED.
**Clarifying compression checks**

The user's requirement mentions checking if the blend file is compressed. They want to skip saving if it's already compressed, which we've handled by checking the header instead of literally opening it in Blender. The compress flag is a user preference for saving, and since we skip when the header shows it's compressed, that works well. For edge cases, Blender uses gzip for its .blend format, which is good. We also output "Total: %* files" in the summary, which just shows the list of args, not a count. I could update the "Usage" message to indicate it will skip if already compressed, but it’s not strictly necessary.
**Summarizing the process**

I can provide a brief summary without including code unless the user requests it, per the instructions. It's important to note that the "skipped" counter increases for existing outputs and for non-blend or already compressed files. I should also clarify that the checks mean it won't save to the output if the file is already compressed. Additionally, I'll include a status update at the top of my message, saying something like, "I added a header check and updated the parser," followed by the summary bullet points—all while keeping it concise.
**Finalizing indentation and output handling**

I need to ensure that indentation is preserved since I used apply_patch to keep the structure intact. It’s worth noting that the script will create "output\filename.blend" to store the compressed copy. However, for files that are already compressed, we won't create an output, which seems to be the intended behavior. Alright, I think I'm ready to finalize everything based on this understanding.</details></think>

---

I added a magic-byte check for gzip compression to the embedded Python and taught the report parser to count these as skipped.

- Changes:
  - New Python helper `is_compressed_file` checks first two bytes for gzip magic and skips saving already-compressed `.blend` files.
  - Emits `SKIP_ALREADY_COMPRESSED:<file>` from Python; the batch parser now counts and reports these under “Skipped”.

- Impact:
  - Already-compressed `.blend` files are not opened/saved; the script moves to the next file.
  - Summary’s “Skipped” now includes already compressed, existing outputs, and non-.blend files.

---

_**User (2025-09-17 19:21Z)**_

@c:\Users\Nathan\Desktop\animd\blender_output.txt it still saved all of them. Only one of them was uncompressed.

---

_**Assistant (default)**_

<think><details><summary>Thought Process</summary>**Debugging compression issues**

I need to troubleshoot the script because it seems to have saved all the files, except for one that wasn't uncompressed. It looks like our gzip magic check didn’t spot the compressed .blend files. I’m wondering if Blender uses gzip or XZ compression. Historically, it appears that Blender started using gzip around version 3.0, replacing the header while maintaining the .blend extension. Many sources suggest that compressed .blend files still begin with the "BLENDER" header, so I should search for confirmation.</details></think>

---

I’m going to verify how Blender marks compressed .blend files so the detection is correct, then adjust the Python check accordingly and update the script.

---

Tool use: **web_search**

<details>
            <summary>Searched web `Blender .blend compressed file header gzip magic or BLENDER header how to detect compression programmatically` • **1** results</summary>
        
| Title | URL | Chunk |
|-------|-----|-------|
| Web Search Results |  | It appears that the script is not correctly identifying compressed `.blend` files, leading to all files being saved regardless of their compression status. This issue may stem from changes in Blender's file compression methods.<br/><br/>**Background:**<br/><br/>Blender transitioned from using Gzip to Zstandard (Zstd) compression starting with version 3.0. This change means that `.blend` files saved with compression in Blender 3.0 and later use the Zstd format, which has a different signature than Gzip. ([docs.blender.org](https://docs.blender.org/manual/en/3.4/files/blend/open_save.html?highlight=compress&utm_source=openai))<br/><br/>**Solution:**<br/><br/>To accurately detect whether a `.blend` file is compressed, the script should check for both Gzip and Zstd signatures. Here's how you can modify the `is_compressed_file` function to account for both compression types:<br/><br/><br/>```python<br/>import struct<br/><br/>def is_compressed_file(filepath):<br/>    with open(filepath, 'rb') as file:<br/>        header = file.read(4)<br/>        # Check for Gzip signature<br/>        if header[:2] == b'\x1f\x8b':<br/>            return True<br/>        # Check for Zstd signature<br/>        elif header == b'\x28\xb5\x2f\xfd':<br/>            return True<br/>    return False<br/>```<br/><br/><br/>**Explanation:**<br/><br/>- **Gzip Signature:** The first two bytes of a Gzip-compressed file are `0x1f` and `0x8b`.<br/>- **Zstd Signature:** The first four bytes of a Zstd-compressed file are `0x28`, `0xb5`, `0x2f`, and `0xfd`. ([projects.blender.org](https://projects.blender.org/blender/blender/commit/2ea66af742b?utm_source=openai))<br/><br/>**Next Steps:**<br/><br/>1. **Update the Script:** Replace the existing `is_compressed_file` function with the modified version above.<br/>2. **Test the Script:** Run the script on a set of `.blend` files, including both compressed and uncompressed ones, to ensure it correctly identifies and skips already compressed files.<br/><br/>By implementing these changes, the script should accurately detect compressed `.blend` files, regardless of whether they use Gzip or Zstd compression, and skip saving them as intended. |

</details>

---

<think><details><summary>Thought Process</summary>**Adjusting file compression detection**

I need to tweak the internal Python function for file detection. The previous change only looked at gzip magic bytes \x1f\x8b, but it seems Blender now uses Zstandard for compression in the "Compress File" option. I remember that Blender 2.80 used gzip, and then by version 3.0, it switched to Zstd.

I'll update the function to check if sources are compressed with either gzip or zstd by looking at their signature bytes. Blender .blend files start with a "BLENDER" string header, but when compressed, they probably don’t include that header.
**Updating compression logic**

It looks like the compressed file header could actually be a zstd or gzip header, which makes detection through signatures viable. I realize we should modify the embedded Python to import gzip, but that might not be necessary anymore. 

We need to fine-tune our logic to avoid opening compressed files. Currently, we're checking if the output exists and if the source is compressed. However, the user reported that it saved all files, which means our is_compressed_file function mistakenly returned false for compressed files. I need to update the check to read 4 bytes for zstd instead of just 2 for gzip.
**Cleaning up unnecessary imports**

I noticed that the code includes an import for gzip, but we're not using it anymore, so it might be best to remove that line. I want to keep the indentation style consistent as the batch file uses spaces, and I need to make sure there are no tabs.

As I check the current file, it turns out we never actually added "import gzip" in the final version. The earlier attempt added an echo line, but the actual imports are just bpy, os, and sys. This means the previous patch didn't apply correctly, and we need to fix that.
**Updating is_compressed_file function**

Great, there's no unused import, so now I need to adjust the is_compressed_file function between lines 48-54 to read 4 bytes and check both zstd and gzip signatures. The batch parser already recognizes SKIP_ALREADY_COMPRESSED and counts those files correctly.

I also want to refine the logic for calculating the reduction percentage and deleting files if savings fall below the threshold. I’ll implement this update to check signatures properly and handle any decompress signatures, ensuring we apply the patch for those lines. Everything looks good to proceed with the updates!
**Applying structured updates**

We need to follow the developer instructions carefully, starting with a status update and executing tool calls in parallel if applicable. This is a single edit, so I'll use functions.apply_patch to make the necessary updates. 

After the changes, optional linting isn't strictly necessary for batch files, but we might want to report the number of .blend files found. I’ll replace the lines reading 2 bytes with an update that checks for 4 bytes instead.

It's also important to handle the possibility that reading the 4 bytes may fail for shorter files. Since the user stated that a script should only be generated upon request, I'll ensure we keep the communication concise. Now, I’ll proceed with the apply_patch call and prepare the status update.</details></think>

---

I'll update the embedded Python `is_compressed_file` to detect both gzip and Zstd headers so already-compressed files are correctly skipped.

---

Tool use: **apply_patch**

<details>
        <summary>Apply patch for A:\1 Amazon_Active_Projects\3 ProjectStructure\compress_blend_files.bat</summary>
      

```diff
*** Begin Patch
*** Update File: A:\1 Amazon_Active_Projects\3 ProjectStructure\compress_blend_files.bat
@@
-echo def is_compressed_file^(path^):
-echo     try:
-echo         with open^(path, 'rb'^) as f:
-echo             return f.read^(2^) == b'\x1f\x8b'
-echo     except Exception:
-echo         return False
+echo def is_compressed_file^(path^):
+echo     try:
+echo         with open^(path, 'rb'^) as f:
+echo             header = f.read^(4^)
+echo             if header[:2] == b'\x1f\x8b':  # gzip
+echo                 return True
+echo             if header == b'\x28\xb5\x2f\xfd':  # zstd
+echo                 return True
+echo         return False
+echo     except Exception:
+echo         return False
*** End Patch
```

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<think><details><summary>Thought Process</summary>**Addressing user report**

The user reported running the script successfully, but it still saved all files, only one being uncompressed. Our previous implementation used gzip, but many Blender versions now favor Zstd. I’ve applied a patch to check the compression method, incorporating more logic to skip already compressed files. However, we might also need to confirm the user is running a script that outputs 'SKIP_ALREADY_COMPRESSED'. Additionally, we should consider the Blender compression settings since newer versions have switched to Zstd as the default.
**Revisiting saving adjustments**

I think we might not need to change the saving process since detection is updated to Zstd, which should help. However, the user’s experience of "it still saved all of them" suggests the skip didn't trigger, possibly due to loading the file before checking. We've added the skip logic correctly, but our previous detection for Zstd was flawed, so I'll instruct them to re-run the test. Also, there's an unnecessary `import gzip` left from earlier code; since it’s not being used anymore, we should remove it to keep the code concise.
**Clarifying imports and file checks**

I noticed earlier that we put `echo import gzip` at line 34, but it seems our current read shows there’s no `import gzip` present after the sys import on the second read. It looks like we added that earlier in a first patch attempt, but it didn’t carry over in the second edit. However, that’s okay since the file reads fine without it. We should also ensure that if the `output_file` already exists, we’ll skip it, even if the source is compressed. Our order should be to check for existing files first and then skip as needed.
**Analyzing user logs and steps**

The user’s log file is located at `c:\Users\Nathan\Desktop\animd\blender_output.txt`, while our script writes to 'blender_output.txt' in the current directory. I wonder if they redirected the output there, but that's not necessary. Next, I’ll suggest they re-run the script. If it still saves all the files, it might signal a failure in compressed detection, especially since Blender files have a 7-byte header for uncompressed files. For compressed files, the magic bytes for zstd or gzip should work. There may be nuances in how zstd compression is handled, but the script should skip already compressed files when processing.
**Finalizing response and code checks**

I want to ensure we don't accidentally save files if the compressed check fails. We added a skip before printing "PROCESSING:". I'll re-check the code around echo escaping since we use special characters like parentheses that need careful handling. I made sure to escape parentheses with `^`. We're doing fine with the header slices, and comments are clear. However, I see a potential bug with `except Exception:` in Windows echo. We should update summary counts and suggest users re-run the script. I’ll mention the detection update to include Zstd and ask if they can share a snippet from `blender_output.txt` for further debugging. Overall, I aim to keep the response minimal yet informative.</details></think>

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- Likely cause: Blender 3.x uses Zstandard, not gzip. I updated the embedded Python to detect both gzip (1F 8B) and Zstd (28 B5 2F FD) magic bytes and skip those files before opening.

Please re-run the batch. If it still saves compressed files, paste a few lines from `blender_output.txt` showing the SKIP/PROCESSING lines so I can adjust further.

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_**User (2025-09-17 19:21Z)**_

Perfect.

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_**Assistant (default)**_

Great! The script should now properly detect and skip already-compressed .blend files (both gzip and Zstd formats) before attempting to open and save them. This will save time and avoid unnecessary processing of files that are already compressed.

The updated detection logic checks for:
- Gzip compression: `1F 8B` magic bytes
- Zstd compression: `28 B5 2F FD` magic bytes

This covers Blender's compression formats across different versions, so the script will only process truly uncompressed files going forward.

---

