Valentina Restrepo Staff Python Developer Raleigh, 27607, United States [email protected] · (919) 555-1846
11 September 2026
Ms. Roisin Kavanagh Director of Engineering Umstead Health Analytics Raleigh, United States
Application for Senior Python Developer, Umstead Health Analytics
Dear Ms. Kavanagh,
I am applying for the Senior Python Developer post at Umstead Health Analytics. I have spent nine years on clinical and genomic data services and currently own the Python platform at Carolina Sequence Labs: 31 repositories, 12 deployed services, and a nightly pipeline that annotates about 2.4 million sequencing records for 14 laboratory sites on CPython 3.13.
The work I would most want to bring over is the runtime migration. When I arrived, the estate ran on four interpreter versions, three of them no longer receiving fixes, and a clean rebuild was not reproducible because every repository kept a hand-edited requirements file. I moved all 31 repositories to locked, hash-verified builds and standardized on 3.12 and then 3.13. The last holdout was a variant caller pinned to an old scientific stack by a vendor's compiled wheels; rather than block the other 30 repositories on it, I isolated it behind a documented interface and ran it in its own container until it could be replaced. A clean rebuild from an empty cache went from about 11 minutes to 3.
Your posting says parts of the platform still run on Python 3.10, which reaches end of life in October 2026 under the annual release schedule published at python.org, and that you would rather hire someone who has done that migration than someone who will learn it here. I have done it twice, in a regulated laboratory setting where the nightly pipeline cannot miss a run. I would also want to work on your ingest layer, because that is where most of the time went both times.
I write typed code with mypy failing the build, carry the on-call rotation for the services I ship, and hold the AWS Certified Developer Associate certification, renewed in February 2026. I can start with four weeks of notice. Thank you for your time.
Sincerely, Valentina Restrepo
Summary
A Python developer cover letter names the interpreter version you shipped on, the system you built or moved, and one measured result. This guide gives you a full adaptable letter, what to write when the posting lists a stack you have not used, and the openings that get a strong file read rather than skimmed.
Python Developer cover letter examples by experience level
A Python developer cover letter is a one-page letter that tells an engineering manager what you built, what it ran on, and what changed because you built it.
The reason it is worth writing is volume. Python roles draw very large application counts, and most letters say the same four things: passionate about Python, strong problem solver, quick learner, team player. A letter opening with a service, an interpreter version and a number is unusual enough to be read to the end.
Guide to a Python developer cover letter
This guide and the corresponding Python developer cover letter example will cover:
- How to structure the letter, paragraph by paragraph
- Why the runtime and the migration belong in the first two paragraphs
- What counts as evidence when your best work is internal
- What to write when the posting lists a framework you have not shipped
- The openings that get a file read rather than skimmed
How to write a Python developer cover letter
| Paragraph | Its job | Length |
|---|---|---|
| Opening | The post, what you own now, and what it runs on | 2 to 3 sentences |
| Evidence | One system, one change, one number, one period of time | 4 to 6 sentences |
| Fit | Something specific from their posting or engineering writing | 3 to 4 sentences |
| Close | Certifications, notice period, thank you | 2 sentences |
Put the interpreter version in the first paragraph
Almost every Python letter says "Python". A smaller number say "Python 3". Very few say which minor version, on what, at what volume.
Write it plainly: "31 repositories and 12 deployed services on CPython 3.13, with a nightly pipeline that annotates about 2.4 million sequencing records." In one sentence the reader knows how current your production experience is, how large the estate was, and what kind of work you are used to.
Then add the sentence hardly anyone can write: the version you were stuck on, and what you did about it.
A Python developer cover letter example you can adapt
Dear Ms. Kavanagh,
I am applying for the Senior Python Developer post at Umstead Health Analytics. I have spent nine years on clinical and genomic data services and currently own the Python platform at Carolina Sequence Labs: 31 repositories, 12 deployed services, and a nightly pipeline that annotates about 2.4 million sequencing records for 14 laboratory sites on CPython 3.13.
The work I would most want to bring over is the runtime migration. When I arrived, the estate ran on four interpreter versions, three of them no longer receiving fixes, and a clean rebuild was not reproducible because every repository kept a hand-edited requirements file. I moved all 31 repositories to locked, hash-verified builds and standardized on 3.12 and then 3.13. The last holdout was a variant caller pinned to an old scientific stack by a vendor's compiled wheels; rather than block the other 30 repositories on it, I isolated it behind a documented interface and ran it in its own container until it could be replaced. A clean rebuild from an empty cache went from about 11 minutes to 3.
Your posting says parts of the platform still run on Python 3.10, which reaches end of life in October 2026 under the annual release schedule published at python.org, and that you would rather hire someone who has done that migration than someone who will learn it here. I have done it twice, in a regulated laboratory setting where the nightly pipeline cannot miss a run. I would also want to work on your ingest layer, because that is where most of the time went both times.
I write typed code with mypy failing the build, carry the on-call rotation for the services I ship, and hold the AWS Certified Developer Associate certification, renewed in February 2026. I can start with four weeks of notice. Thank you for your time.
Sincerely, Valentina Restrepo
Openings that work
| Instead of | Use |
|---|---|
| I am passionate about Python and love writing clean code | I own 31 repositories and 12 deployed services on CPython 3.13 at a clinical genomics laboratory |
| I am writing to express my interest in your Python developer position | I am applying for the Senior Python Developer post, and the migration in your posting is work I have done twice |
| I have strong problem-solving skills and attention to detail | A clean rebuild went from about 11 minutes to 3 after I moved 31 repositories to locked builds |
What counts as evidence in a Python cover letter
Most of the best Python work is internal and cannot be linked to. None of the evidence below requires a public repository.
| Kind of evidence | What it looks like in a sentence |
|---|---|
| Runtime migration | Moved 6 services from CPython 3.9 to 3.12 in eleven weeks, unpinning 23 dependencies |
| Performance | Replaced a row-by-row pandas loop with a chunked vectorized pass; the nightly job fell from 4 hours to 38 minutes |
| Test coverage that caught something | Took a package from 31 to 88 percent coverage, catching the malformed-manifest defect before release |
| Open source | 14 merged pull requests to a validation library since 2023, including a timezone parsing fix in release 2.4 |
Pick one. A single well-told change beats a list of six, because the reader is deciding whether to spend an hour interviewing you, not scoring a checklist.
When the posting lists a stack you have not shipped
Python postings name a framework, a cloud, a queue and a data library, and almost nobody has shipped all four in that combination.
Name the closest thing you have shipped and say what transfers, in one sentence: "I have run Celery rather than Airflow, so scheduling, retries and backfill are familiar and the operator model is what I would need to learn." Say which of their listed technologies you have used in production and which you have only read about. Lead with the part of the posting you match best.
Do not claim a framework you have only followed a tutorial in; one question about its failure modes will expose it. Do not apologize for gaps or spend a paragraph on what you lack. Do not paste the posting's technology list back at them. Do not send a letter with no company name in it, and do not call yourself passionate, dedicated or a self-starter.
The occupation is growing, and the interpreter still turns over every October
Employment of software developers, quality assurance analysts and testers is projected to grow 10 percent between 2025 and 2035, much faster than average, with about 106,100 openings projected each year over the decade and a median annual wage of $135,980 for software developers in May 2025 (BLS Occupational Outlook Handbook, May 2025 wages and 2025 to 2035 projections, published 27 August 2026).
Meanwhile PEP 602 at python.org puts a new Python feature release in October every year, each supported for five years in total, so one interpreter version leaves support every year on a published date whether or not the services running on it have moved. A growing occupation with a fixed annual deadline is the market in which a migration paragraph outperforms a paragraph about your learning style.
Length, format and sending it
One page, four paragraphs, 250 to 400 words. PDF unless the portal says otherwise, named for yourself and the role: valentina-restrepo-python-developer-cover-letter.pdf.
Address a person. Engineering leadership is usually findable on a team page or an engineering blog, and "Dear Hiring Manager" on an otherwise specific file reads as a letter sent to thirty companies.
Use the same numbers as your resume. Our Python developer resume example uses the figures here, and the free ATS checker will tell you whether the pair parse cleanly.
Key takeaways
- Name the interpreter version and the estate in the first paragraph.
- Spend the second paragraph on one change, with a before, an after and a duration.
- Say which dependency pinned you and what you did about it.
- Quote something real from their posting or their engineering writing.
- Be honest about technologies you have only read about.
- One page, four paragraphs, addressed to a named person.
- Use the same figures as the resume, so the pair never contradicts itself.
Write your Python developer cover letter in 10 minutes with our AI cover letter builder.
Python developer cover letter questions, answered
How long should a Python developer cover letter be?
One page, four paragraphs, 250 to 400 words. Managers read these in batches, and length does not read as effort.
Do I need a cover letter if the application is just a form and a resume?
Attach one wherever there is a field for it. The form collects the same structured data from every candidate. The letter is the only place you can say which migration you ran and why you would do it again at their company.
Should I put a link to my code in the letter?
One link, with one sentence saying what is in it. A bare profile link is worth very little; "14 merged pull requests to a manifest validation library since 2023, including the timezone-naive parsing fix" tells the reader whether it is worth opening.
What do I write with no professional Python experience yet?
Write one project the way this guide describes a system: what it does, what interpreter and packaging it uses, how much data it handles, how it is tested, and what it replaced. Then say what you would want to work on at their company. One project at that depth outperforms a paragraph about enthusiasm.
Should I mention the Python version in a cover letter, or is that too technical?
Mention it. Several minor versions are separately maintained at any time, each on a published five-year support schedule set by PEP 602 at python.org, so the version you shipped on is a compact way of saying how recent your production experience is. To the person who maintains the codebase it reads as precision, not pedantry.