Excel Automation

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

For an image or scan of a paper form that needs editable cells and a printable layout, load Printable forms before creating the workbook. Follow the host's designated spreadsheet authoring tool; use the openpyxl examples below only when that tool is permitted.

Quick Start

Before a command brings Excel forward or changes its visible window, check user activity and other agents' occupancy. Use only foreground operations covered by the current task's authorization. If the surface is in use, occupancy is unknown, or unexpected input occurs, stop input and continue independent background work.

# 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

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)

Apply these colors to financial reports using that convention. For a paper form, preserve its intended print appearance; do not add input colors by default.

Core Formatting Patterns

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

Conditional Formatting (Sensitivity Tables)

Red-to-green gradient for sensitivity analysis:

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

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

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

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

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":

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

# 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:

# 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

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