CSV
Polars for Large CSV Processing Beyond Memory Limits
Use Polars lazy scanning to filter and group a large CSV without loading it whole, set column types so zip codes stay text, and write Parquet as you go.
6 min read
Tag
python
134 posts
YAML
Round Tripping YAML Without Losing Comments or Order
Edit a YAML file in code and keep its comments, anchors and quotes. PyYAML drops them, ruamel.yaml and yq keep them, and each changes some whitespace.
6 min read
XML
Running XSLT in Python With lxml and What It Reports
Compile a stylesheet once with lxml, pass parameters safely, read xsl:message from the error log, block file and network reads, and know the 1.0 limit.
7 min read
CSV
Handling CSV With Comment Lines and Metadata Headers
Some CSV files carry lines starting with a hash that are notes, not data. Skip them safely, because a comment option can also cut values like Suite #4.
6 min read
CSV
Header Variants and Normalizing Column Names in CSV Files
Clean up messy CSV headers into stable column names: BOMs, spaces, case, accents, duplicates, blanks and leading digits, with a function you can test.
7 min read
CSV
Fixed Width Files and Converting Them to CSV Safely
Convert a fixed width file to CSV by slicing each line at known positions, check every line length, and handle implied decimals, padding and wide characters.
7 min read
Excel
Protecting a Generated Workbook From Accidental Edits
Lock the cells, sheets and structure of a workbook your script generates so readers cannot break formulas, with openpyxl and XlsxWriter, and know the limits.
7 min read
Excel
Watching a Folder for New Excel Files and Importing Them
Watch a folder for new Excel files and import each once: polling or watchdog, waiting for the copy to finish, moving files, idempotent loads and failures.
7 min read
Excel
Splitting One Excel Sheet Into a Workbook per Group
Split one Excel sheet into a workbook per region or customer with pandas groupby, safe file names, formatting, a manifest and checks that the parts add up.
7 min read
Excel
Merging Hundreds of Workbooks Into One Table With Python
Combine hundreds of Excel files into one table with Python: glob, read each sheet, check headers, add the source name, quarantine bad files and verify counts.
7 min read
Excel
Automating Weekly Excel Reports With Python and cron
Build a weekly Excel report with Python: query the database, write the workbook, email it and schedule it with cron, with paths, logs, locks and failures.
7 min read
Excel
How Running a Python Script From Excel With xlwings Works
Run Python from an Excel button with xlwings: install, quickstart, RunPython and RunPython, read and write ranges, user defined functions and the limits.
7 min read