# strif

Strif is a tiny (\~1000 loc) library of \~30 string, file, and object utilities for
modern Python. It has **zero dependencies**.

It is simply a few functions and tricks that have repeatedly shown value in various
projects. The goal is not to give a comprehensive suite of utilities but simply to
complement the standard libraries and fill in a few gaps.

> [!TIP]
> 
> ✨ **NEW:** **Version 3.1** adds `atomic_write_text()`/`atomic_write_bytes()`, exposes
> `__version__`, and supports Python 3.10-3.14. ✨
>
> If you're using strif, you might also want to check out
> [prettyfmt](https://github.com/jlevy/prettyfmt), another small library built on strif
> that has some extra functions for pretty, human-readable outputs for objects, sizes,
> times and dates, etc.

> [!TIP]
> 
> Given the rapid rise of supply chain attacks on Python packages, it's worth noting this
> repository has **ZERO dependencies**. You can even have your agent review its security
> before you use it.

## Why Use strif (Especially with Coding Agents)

Strif is a simple way to get better Python out of coding agents. It's small enough that
once you tell an agent to use it, it adopts it consistently—so you can enforce good habits
like atomic file writes, sortable timestamped ids, and stable hashing instead of hoping
the agent reinvents them correctly each time. A prompt as simple as this is usually enough:

> Run `uv add strif` and review its docs, then always use it for atomic file writes,
> timestamps and ids, and similar best practices from now on.

The whole library (all zero-dependency):

- **Atomic file operations** with parent-dir creation and optional backups, so an
  interrupted or crashed run never leaves a partial or corrupt file in its final location.
  See `atomic_output_file()`, `atomic_write_text()`, `atomic_write_bytes()`,
  `copyfile_atomic()`.

- **Random and timestamped ids** in **base 36** (concise, case-insensitive, filename-safe),
  including ISO-timestamped ids that sort by creation time.
  See `new_uid()`, `new_timestamped_uid()`.

- **File and string hashing** with convenient hex, base36, and base64 outputs—good for
  cache keys and dedup. See `hash_string()`, `hash_file()`, `file_mtime_hash()`.

- **An `AtomicVar` type**: a thread-safe variable (an `RLock` around any value) that makes
  correct concurrent access the easy path.

- **String utilities** for replacing or inserting multiple substrings at once and for
  validated, type-checked string templates.
  See `StringTemplate`, `replace_multiple()`, `insert_multiple()`.

- **Abbreviate and quote strings** for clean logging and display.
  See `abbrev_str()`, `single_line()`, `quote_if_needed()`.

That's all! They are all quite simple and small, so see the pydoc strings or code for
full docs.

## Installation

```sh
# Use uv
uv add strif
# Or poetry
poetry add strif
# Or pip
pip install strif
```

## Text Abbreviations and Formatting

- **`abbrev_str(string: str, max_len: Optional[int] = 80, indicator: str = '…')`**

  Abbreviates a string and appends an indicator if the content exceeds the allowed
  length.

- **`abbrev_list(items: List[Any], max_items: int = 10, item_max_len: Optional[int] =
  40, joiner: str = ', ', indicator: str = '…')`**

  Shortens each element of a list and appends an ellipsis if the list is truncated.

- **`single_line(text: str)`**

  Converts multi-line text into a single line by replacing extra whitespace with spaces.

- **`quote_if_needed(arg: Any)`**

  Returns a string with quotes if needed for proper display (for example, for filenames
  with spaces).

## String Identifiers, Timestamps, and Hashing

> [!TIP]
> 
> These functions use [base 36](https://en.wikipedia.org/wiki/Base36). If you need a
> readable, concise identifier, api key format, or hash format, consider base 36. In my
> humble opinion, base 36 ids are underrated and should be used more often:
> 
> - Base 36 is briefer than hex and yet avoids ugly non-alphanumeric characters.
>
> - Base 36 is case insensitive.
>   If you use identifiers for filenames, you definitely should prefer case insensitive
>   identifiers because of case-insensitive filesystems (like macOS).
>
> - Base 36 is easier to read aloud over the phone for an auth code or to type manually.
>
> - Base 36 is only `log(64)/log(36) - 1 = 16%` longer than base 64.
> 

- **`new_uid(bits: int = 64)`**

  Generates a random base36 alphanumeric string with at least the specified bits of
  randomness. Suitable for filenames (especially on case-insensitive filesystems).
  Uses `random.SystemRandom()` for randomness.

- **`new_timestamped_uid(bits: int = 32)`**

  Creates a unique ID starting with an ISO timestamp, then fractions of seconds and bits
  of randomness. *Example*: `20150912T084555Z-378465-43vtwbx`

- **`iso_timestamp(microseconds: bool = True)`**

  Returns an ISO 8601 timestamp in UTC, e.g. `2015-09-12T08:41:12.397217Z` (with
  microseconds) or `2015-09-12T08:41:12Z` (without).

- **`format_iso_timestamp(datetime_obj: datetime, microseconds: bool = True)`**

  Formats a given datetime object as an ISO 8601 timestamp, ensuring UTC formatting with
  a trailing Z.

- **`clean_alphanum(string: str, max_length: Optional[int] = None)`**

  Converts a string to a clean identifier by keeping only the first alphanumeric
  characters and replacing others with underscores.

- **`clean_alphanum_hash(string: str, max_length: int = 64, max_hash_len: Optional[int]
  = None)`**

  Combines the cleaned version of a string with a base36 SHA1 hash to minimize
  collisions.

## File Hashing

- **`file_mtime_hash(path: str | Path)`**

  Computes a fast hash using a file's name, size, and high-resolution modification time,
  without looking at file contents.
  A useful key for fast caching of file contents.

- **`hash_string(string: str, algorithm: str = 'sha1') -> Hash`** and
  **`hash_file(file_path: str | Path, algorithm: str = 'sha1') -> Hash`**

  Provide flexible hashing mechanisms.
  The returned `Hash` object has properties to output the digest in hexadecimal, base36,
  or with a prefixed algorithm name.

## Atomic File Operations with Optional Backups

> [!TIP]
> 
> It’s generally good practice when creating files to write to a file with a temporary
> name, and move it to a final location once the file is complete.
> This way, you never leave partial, incorrect versions of files in a directory due to
> interruptions or failures.

- **`atomic_output_file(dest_path: str | Path, make_parents: bool = False,
  backup_suffix: Optional[str] = None, tmp_suffix: str = '.partial')`**

  A context manager for writing files or directories atomically.
  A temporary file is created and, upon successful completion, renamed to the target
  location.

- **`copyfile_atomic(source_path: str | Path, dest_path: str | Path, make_parents: bool
  = False, backup_suffix: Optional[str] = None)`**

  Atomically copies a file while preserving its timestamps.

- **`copytree_atomic(source_path: str | Path, dest_path: str | Path, make_parents: bool
  = False, backup_suffix: Optional[str] = None, symlinks: bool = False)`**

  Recursively copies a directory or file atomically.

- **`move_to_backup(path: str | Path, backup_suffix: str = '{timestamp}.bak')`** and
  **`copy_to_backup(path: str | Path, backup_suffix: str = '{timestamp}.bak')`**

  Functions to move or copy an existing file or directory to a backup destination.

- **`move_file(src_path: Path, dest_path: Path, keep_backup: bool = True, backup_suffix:
  str = '{timestamp}.bak')`**

  Moves a file to a new location, automatically creating parent directories and
  optionally keeping a backup of the destination if it already exists.

- **`atomic_write_text(dest_path, text, make_parents=False, backup_suffix=None,
  encoding='utf-8')`** and **`atomic_write_bytes(dest_path, data, make_parents=False,
  backup_suffix=None)`**

  Convenience wrappers around `atomic_output_file()` for the common case of writing a
  whole string or bytes value atomically in a single call.

For example, it is generally a good idea to wrap an `open()` call with
`atomic_output_file()`:

```python
with atomic_output_file("some-dir/my-final-output.txt") as temp_target:
    with open(temp_target, "w") as f:
        f.write("some contents")
```

Or, for the common whole-value case, just:

```python
atomic_write_text("some-dir/my-final-output.txt", "some contents")
```

And this can (and in most cases should) be used in place of `shutil.copyfile`:

```python
copyfile_atomic(source_path, dest_path, make_parents=True, backup_suffix=None)
```

Now if there is some issue during write, the output will instead be at a temporary
location in the same directory (with a name like
`some-dir/my-final-output.txt.partial.XXXXX`.) This ensures integrity of the file
appearing in the final location.

There are also some handy additional options:

```python
with atomic_output_file("some-dir/my-final-output.txt",
                        make_parents=True, backup_suffix=".old.{timestamp}") as temp_target:
    with open(temp_target, "w") as f:
        f.write("some contents")
```

This creates parent folders as needed (a major convenience).
And if you would have clobbered a previous output, it keeps a backup with a (fixed or
uniquely timestamped) suffix.

Used judiciously, these options can save boilerplate coding and avoid debugging ugly
corner case failures with zero-length or truncated files.

## Syntax Sugar for Temporary Files

Syntax sugar for auto-deleting temporary files or directories using `with`:

```python
with temp_output_file("my-scratch.") as (fd, path):
    # Do a bunch of stuff with the opened file descriptor or path, knowing
    # it will be removed assuming successful termination.


with temp_output_dir("work-dir.", dir="/var/tmp") as work_dir:
    # Create some files in the now-existing path work_dir, and it will be
    # deleted afterwards.
```

Note these don’t delete files in case of error, which is usually what you want.
Add `always_clean=True` if you want the temporary file or directory to be removed no
matter what.

## Atomic Vars

`AtomicVar` is a simple zero-dependency thread-safe variable that works for any type.
It simply combines a value with reentrant lock (`threading.RLock`) to make thread-safe
use of the variable less error prone.

Often the standard "Pythonic" approach is to use locks directly, but for some common use
cases, `AtomicVar` may be simpler and more readable.
Works on any type, including lists and dicts.

Other options include `threading.Event` (for shared booleans), `threading.Queue` (for
producer-consumer queues), and `multiprocessing.Value` (for process-safe primitives).

Examples:

```python
# Immutable types are always safe:
count = AtomicVar(0)
count.update(lambda x: x + 5)  # In any thread.
count.set(0)  # In any thread.
current_count = count.value  # In any thread.

# Useful for flags:
global_flag = AtomicVar(False)
global_flag.set(True)  # In any thread.
if global_flag:  # In any thread.
    print("Flag is set")


# For mutable types,consider using `copy` or `deepcopy` to access the value:
my_list = AtomicVar([1, 2, 3])
my_list_copy = my_list.copy()  # In any thread.
my_list_deepcopy = my_list.deepcopy()  # In any thread.

# For mutable types, the `updates()` context manager gives a simple way to
# lock on updates:
with my_list.updates() as value:
    value.append(5)

# Or if you prefer, via a function:
my_list.update(lambda x: x.append(4))  # In any thread.

# You can also use the var's lock directly. In particular, this encapsulates
# locked one-time initialization:
initialized = AtomicVar(False)
with initialized.lock:
    if not initialized:  # checks truthiness of underlying value
        expensive_setup()
        initialized.set(True)

# Or:
lazy_var: AtomicVar[list[str] | None] = AtomicVar(None)
with lazy_var.lock:
    if not lazy_var:
            lazy_var.set(expensive_calculation())
```

## Simple String Template

A validated template string that supports only specified fields.
Can subclass to have a type with a given set of `allowed_fields`. Provide a type with a
field name to allow validation of int/float format strings.

Examples:

```python
>>> t = StringTemplate("{name} is {age} years old", ["name", "age"])
>>> t.format(name="Alice", age=30)
'Alice is 30 years old'

>>> t = StringTemplate("{count:3d}@{price:.2f}", [("count", int), ("price", float)])
>>> t.format(count=10, price=19.99)
' 10@19.99'
```

## Multiple String Replacements

`Insertion` and `Replacement` are `NamedTuple`s, so you can use named fields
(`Insertion(offset, text)`, `Replacement(start, end, text)`) or plain positional tuples.

- **`insert_multiple(text: str, insertions: list[Insertion]) -> str`**

  Insert multiple strings into `text` at the given offsets, at once.

- **`replace_multiple(text: str, replacements: list[Replacement]) -> str`**

  Replace multiple substrings in `text` with new strings, simultaneously.
  Each `Replacement` is `(start_offset, end_offset, new_string)`.

## FAQ

### Why bother, if it’s so short?

Because it saves time, saves you stupid bugs and clumsy repetition, and has zero (yes
zero) dependencies.

### Are there other libraries that offer these utilities?

A few yes.
Some support has improved in Python 3; for example `textwrap.shorten()` can be
used instead of `abbrev_str()` (that said, strif also offers `abbrev_list()`).

[boltons](https://github.com/mahmoud/boltons) is a much larger library of general
utilities. strif is intended to be much smaller.
The [atomicwrites](https://github.com/untitaker/python-atomicwrites) library is similar
to `atomic_output_file()` but is no longer maintained.
For some others like the base36 tools I haven't seen equivalents elsewhere.

If you don't want the dependency on strif, also feel free to just copy the bit you want!
They're short.

### Is it mature?

I’ve used many of these functions in production situations for years.
We don't have comprehensive tests currently.
But they're mostly so small you can inspect them yourself.

* * *

## Development

For how to install uv and Python, see [installation.md](docs/installation.md).

For development workflows, see [development.md](docs/development.md).

For instructions on publishing to PyPI, see [publishing.md](docs/publishing.md).

* * *

*This project was built from
[simple-modern-uv](https://github.com/jlevy/simple-modern-uv).*