---
name: excel-automation
description: 'Create, parse, and control Excel files on macOS. Professional formatting with openpyxl, complex xlsm parsing with stdlib zipfile+xml for investment bank financial models, and Excel window control via AppleScript. Use when creating formatted Excel reports, parsing financial models that openpyxl cannot handle, or automating Excel on macOS.'
version: "1.0.0"
author: "seaworld008"
source: "in-house"
source_url: ""
tags: '["automation", "excel"]'
created_at: "2026-03-04"
updated_at: "2026-03-20"
quality: 5
complexity: "intermediate"
---

# Excel Automation

Create professional Excel files, parse complex financial models, and control Excel on macOS.

## Quick Start

```bash
# Create a formatted Excel report
uv run --with openpyxl scripts/create_formatted_excel.py output.xlsx

# Parse a complex xlsm that openpyxl can't handle
uv run scripts/parse_complex_excel.py model.xlsm              # List sheets
uv run scripts/parse_complex_excel.py model.xlsm "DCF"        # Extract a sheet
uv run scripts/parse_complex_excel.py model.xlsm --fix        # Fix corrupted names

# Control Excel via AppleScript (with timeout to prevent hangs)
timeout 5 osascript -e 'tell application "Microsoft Excel" to activate'
```

## Overview

Three capabilities:

| Capability | Tool | When to Use |
|-----------|------|-------------|
| **Create** formatted Excel | `openpyxl` | Reports, mockups, dashboards |
| **Parse** complex xlsm/xlsx | `zipfile` + `xml.etree` | Financial models, VBA workbooks, >1MB files |
| **Control** Excel window | AppleScript (`osascript`) | Zoom, scroll, select cells programmatically |

## Tool Selection Decision Tree

```
Is the file simple (data export, no VBA, <1MB)?
├─ YES → openpyxl or pandas
└─ NO
   ├─ Is it .xlsm or from investment bank / >1MB?
   │   └─ YES → zipfile + xml.etree.ElementTree (stdlib)
   └─ Is it truly .xls (BIFF format)?
       └─ YES → xlrd
```

**Signals of "complex" Excel**: file >1MB, `.xlsm` extension, from investment bank/broker, contains VBA macros.

**IMPORTANT**: Always run `file <path>` first — extensions lie. A `.xls` file may actually be a ZIP-based xlsx.

## Creating Excel Files (openpyxl)

### Professional Color Convention (Investment Banking Standard)

| Color | RGB Code | Meaning |
|-------|----------|---------|
| Blue | `0000FF` | User input / assumption |
| Black | `000000` | Calculated value |
| Green | `008000` | Cross-sheet reference |
| White on dark blue | `FFFFFF` on `4472C4` | Section headers |
| Dark blue text | `1F4E79` | Title |

### Core Formatting Patterns

```python
from openpyxl.styles import Font, PatternFill, Border, Side, Alignment

# Fonts
BLUE_FONT = Font(color="0000FF", size=10, name="Calibri")
BLACK_FONT_BOLD = Font(color="000000", size=10, name="Calibri", bold=True)
GREEN_FONT = Font(color="008000", size=10, name="Calibri")
HEADER_FONT = Font(color="FFFFFF", size=12, name="Calibri", bold=True)

# Fills
DARK_BLUE_FILL = PatternFill("solid", fgColor="4472C4")
LIGHT_BLUE_FILL = PatternFill("solid", fgColor="D9E1F2")
INPUT_GREEN_FILL = PatternFill("solid", fgColor="E2EFDA")
LIGHT_GRAY_FILL = PatternFill("solid", fgColor="F2F2F2")

# Borders
THIN_BORDER = Border(bottom=Side(style="thin", color="B2B2B2"))
BOTTOM_DOUBLE = Border(bottom=Side(style="double", color="000000"))
```

### Number Format Codes

| Format | Code | Example |
|--------|------|---------|
| Currency | `'$#,##0'` | $1,234 |
| Currency with decimals | `'$#,##0.00'` | $1,234.56 |
| Percentage | `'0.0%'` | 12.3% |
| Percentage (2 decimal) | `'0.00%'` | 12.34% |
| Number with commas | `'#,##0'` | 1,234 |
| Multiplier | `'0.0x'` | 1.5x |

### Conditional Formatting (Sensitivity Tables)

Red-to-green gradient for sensitivity analysis:

```python
from openpyxl.formatting.rule import ColorScaleRule

rule = ColorScaleRule(
    start_type="min", start_color="F8696B",   # Red (low)
    mid_type="percentile", mid_value=50, mid_color="FFEB84",  # Yellow (mid)
    end_type="max", end_color="63BE7B"         # Green (high)
)
ws.conditional_formatting.add(f"B2:F6", rule)
```

### Execution

```bash
uv run --with openpyxl scripts/create_formatted_excel.py
```

Full template script: See `scripts/create_formatted_excel.py`

## Parsing Complex Excel (zipfile + xml)

When openpyxl fails on complex xlsm files (corrupted DefinedNames, complex VBA), use stdlib directly.

### XLSX Internal ZIP Structure

```
file.xlsx (ZIP archive)
├── [Content_Types].xml
├── xl/
│   ├── workbook.xml          ← Sheet names + order
│   ├── sharedStrings.xml     ← All text values (lookup table)
│   ├── worksheets/
│   │   ├── sheet1.xml        ← Cell data for sheet 1
│   │   ├── sheet2.xml        ← Cell data for sheet 2
│   │   └── ...
│   └── _rels/
│       └── workbook.xml.rels ← Maps rId → sheetN.xml
└── _rels/.rels
```

### Sheet Name Resolution (Two-Step)

Sheet names in `workbook.xml` link to physical files via `_rels/workbook.xml.rels`:

```python
import zipfile
import xml.etree.ElementTree as ET

MAIN_NS = 'http://schemas.openxmlformats.org/spreadsheetml/2006/main'
REL_NS = 'http://schemas.openxmlformats.org/officeDocument/2006/relationships'
RELS_NS = 'http://schemas.openxmlformats.org/package/2006/relationships'

def get_sheet_path(zf, sheet_name):
    """Resolve sheet name to physical XML file path inside ZIP."""
    # Step 1: workbook.xml → find rId for the sheet name
    wb_xml = ET.fromstring(zf.read('xl/workbook.xml'))
    sheets = wb_xml.findall(f'.//{{{MAIN_NS}}}sheet')
    rid = None
    for s in sheets:
        if s.get('name') == sheet_name:
            rid = s.get(f'{{{REL_NS}}}id')
            break
    if not rid:
        raise ValueError(f"Sheet '{sheet_name}' not found")

    # Step 2: workbook.xml.rels → map rId to file path
    rels_xml = ET.fromstring(zf.read('xl/_rels/workbook.xml.rels'))
    for rel in rels_xml.findall(f'{{{RELS_NS}}}Relationship'):
        if rel.get('Id') == rid:
            return 'xl/' + rel.get('Target')

    raise ValueError(f"No file mapping for {rid}")
```

### Cell Data Extraction

```python
def extract_cells(zf, sheet_path):
    """Extract all cell values from a sheet XML."""
    # Build shared strings lookup
    shared = []
    try:
        ss_xml = ET.fromstring(zf.read('xl/sharedStrings.xml'))
        for si in ss_xml.findall(f'{{{MAIN_NS}}}si'):
            texts = si.itertext()
            shared.append(''.join(texts))
    except KeyError:
        pass  # No shared strings

    # Parse sheet cells
    sheet_xml = ET.fromstring(zf.read(sheet_path))
    rows = sheet_xml.findall(f'.//{{{MAIN_NS}}}row')

    data = {}
    for row in rows:
        for cell in row.findall(f'{{{MAIN_NS}}}c'):
            ref = cell.get('r')         # e.g., "A1"
            cell_type = cell.get('t')   # "s" = shared string, None = number
            val_el = cell.find(f'{{{MAIN_NS}}}v')

            if val_el is not None and val_el.text:
                if cell_type == 's':
                    data[ref] = shared[int(val_el.text)]
                else:
                    try:
                        data[ref] = float(val_el.text)
                    except ValueError:
                        data[ref] = val_el.text
    return data
```

### Fixing Corrupted DefinedNames

Investment bank xlsm files often have corrupted `<definedName>` entries containing "Formula removed":

```python
def fix_defined_names(zf_in_path, zf_out_path):
    """Remove corrupted DefinedNames and repackage."""
    import shutil, tempfile
    with tempfile.TemporaryDirectory() as tmp:
        tmp = Path(tmp)
        with zipfile.ZipFile(zf_in_path, 'r') as zf:
            zf.extractall(tmp)

        wb_xml_path = tmp / 'xl' / 'workbook.xml'
        tree = ET.parse(wb_xml_path)
        root = tree.getroot()

        ns = {'main': MAIN_NS}
        defined_names = root.find('.//main:definedNames', ns)
        if defined_names is not None:
            for name in list(defined_names):
                if name.text and "Formula removed" in name.text:
                    defined_names.remove(name)

        tree.write(wb_xml_path, encoding='utf-8', xml_declaration=True)

        with zipfile.ZipFile(zf_out_path, 'w', zipfile.ZIP_DEFLATED) as zf:
            for fp in tmp.rglob('*'):
                if fp.is_file():
                    zf.write(fp, fp.relative_to(tmp))
```

Full template script: See `scripts/parse_complex_excel.py`

## Controlling Excel on macOS (AppleScript)

All commands verified on macOS with Microsoft Excel.

### Verified Commands

```bash
# Activate Excel (bring to front)
osascript -e 'tell application "Microsoft Excel" to activate'

# Open a file
osascript -e 'tell application "Microsoft Excel" to open POSIX file "/path/to/file.xlsx"'

# Set zoom level (percentage)
osascript -e 'tell application "Microsoft Excel"
    set zoom of active window to 120
end tell'

# Scroll to specific row
osascript -e 'tell application "Microsoft Excel"
    set scroll row of active window to 45
end tell'

# Scroll to specific column
osascript -e 'tell application "Microsoft Excel"
    set scroll column of active window to 3
end tell'

# Select a cell range
osascript -e 'tell application "Microsoft Excel"
    select range "A1" of active sheet
end tell'

# Select a specific sheet by name
osascript -e 'tell application "Microsoft Excel"
    activate object sheet "DCF" of active workbook
end tell'
```

### Timing and Timeout

Always add `sleep 1` between AppleScript commands and subsequent operations (e.g., screenshot) to allow UI rendering.

**IMPORTANT**: `osascript` will hang indefinitely if Excel is not running or not responding. Always wrap with `timeout`:

```bash
# Safe pattern: 5-second timeout
timeout 5 osascript -e 'tell application "Microsoft Excel" to activate'

# Check exit code: 124 = timed out
if [ $? -eq 124 ]; then
    echo "Excel not responding — is it running?"
fi
```

## Common Mistakes

| Mistake | Correction |
|---------|-----------|
| openpyxl fails on complex xlsm → try monkey-patching | Switch to `zipfile` + `xml.etree` immediately |
| Count Chinese characters with `wc -c` | Use `wc -m` (chars, not bytes; Chinese = 3 bytes/char) |
| Trust file extension | Run `file <path>` first to confirm actual format |
| openpyxl `load_workbook` hangs on large xlsm | Use `zipfile` for targeted extraction instead of loading entire workbook |

## Important Notes

- Execute Python scripts with `uv run --with openpyxl` (never use system Python)
- LibreOffice (`soffice --headless`) can convert formats and recalculate formulas
- Detailed formatting reference: See `references/formatting-reference.md`
