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Current version: 0.3.x

This library provides Python-like string formatting for javascript.

Exports the function pystringformat to the global scope if run in a browser, or the module pystringformat if run in node.js.

Example usage:

var fmt = require("pystringformat");
// if loaded bare-bone into a browser:
//    var fmt = window.pystringformat;

fmt("Hello, {}", "world");  // "Hello, world"
fmt("{0:d} in decimal is {0:x} in hexadecimal. ", 32);  // "32 in decimal is 20 in hexadecimal. "
fmt("There are only {0:b} types of people...", 2);  // "There are only 10 types of people..."
fmt("Numbers can be padded {:6d}", 123); // "Numbers can be padded    123"
fmt("{0} plus {0} equals {1}", "two", "four");  // "two plus two equals four"
fmt("{:.4f}", 1.232));  // "1.2320";
fmt("{:10.4f}", 1.232);  // "    1.2320"

fmt("{a.x}", {a: {x: 2}});             // 2
fmt("{a.b[1]}", {a: {b: [1, 2, 3]}})); // 2

Supports a subset of the String.format of python 2 See for documentation

Supported codes:

  • s - string
  • c - char from integer
  • d - decimal
  • o - octal
  • x - hex
  • X - uppercase hex
  • b - binary
  • f - fixed point
  • F - same as f
  • % - multiply by 100, and show with fixed 'f' format precision

If the argument after the format string is one Object it can be used as a dictionary.

Known and deliberate differences from Python:

  • Without width or format specifiers, all objects are coerced to string by default.
  • Boolean can be formatted with 's' code, and is also by default. In the Python implementation, it depends on the formatting string (not only the code)
  • The 'f' code will at some point switch to exponential representation
  • The 'n' code is left out, because the locale would have to be set explicitly
  • The 'g' and 'G' codes are left out, since the semantics don't really make sense for javascript
  • Bracket and dot notations are interchangeable (javascript only has one type of properties)


Version 0.3.0

A small cleanup years later, April 2017. Exporting function like a standard node module now, and window.pystringformat export only happens when loaded in a browser. Got rid of Bower and Grunt (kind of overkill for this) and replaced jasmine with mocha.

Version 0.2.2

Fixed some cases where having arguments looking like format strings would mess up things. Example:

fmt("{}, {}!", "Hello, {}", "world"); // Should be "Hello, {}, world!"

Heavy refactoring.

Version 0.2.1

No changes, updated the version number to see an update on

Version 0.2

  • A single object can be used as a dictionary