Simple string parsing and formatting using Python's format strings
Project description
fTmplt
Simple string parsing and formatting using Python's format strings
This project is similar to parse, but emphasizes on format strings that are both parsable and formattable. This means only format specifiers that are both valid for parsing and formatting are supported. It was originally developed to parse and format input and output files for various computational physics libraries.
Installation
pip install git+https://github.com/dylanljones/ftmplt.git
Format Specification
The full format()
Format Specification Mini-Language with all types
is supported:
[[fill]align][sign][0][width][.precision][type]
Type | Description | Output |
---|---|---|
None | Unformatted strings | str |
d | Decimal integer | int |
b | Binary integer | int |
o | Octal integer | int |
x | Hex integer | int |
f | Fixed point floating point | float |
e | Floating-point numbers with exponent | float |
g | General number format (either d, f or e) | float |
% | Percentage | float |
Additionally, datetime
objects can be parsed and formatted using the strftime()
Format Codes.
The differences between parse()
and format()
are:
- The align operators will cause spaces (or specified fill character) to be stripped from the parsed value. The width is not enforced; it just indicates there may be whitespace or "0"s to strip.
- Numeric parsing will automatically handle a "0b", "0o" or "0x" prefix. That is, the "#" format character is handled automatically by d, b, o and x formats. For "d" any will be accepted, but for the others the correct prefix must be present if at all.
- The "e" and "g" types are case-insensitive so there is not need for the "E" or "G" types. The "e" type handles Fortran formatted numbers (no leading 0 before the decimal point).
Usage
Define a template using the Python format string syntax. From there it's a simple thing to parse, search or format a string.
>>> import ftmplt
>>> template = "Hello, my name is {name} and I am {age:d} years old."
Format the template string:
>>> text = ftmplt.format(template, name="John", age=42)
>>> text
'Hello, my name is John and I am 42 years old.'
Parse all parameters from the string:
>>> ftmplt.parse(template, text)
{'name': 'John', 'age': 42}
or search a string for some pattern:
>>> ftmplt.search(template, text, "name")
('John', (19, 23))
>>> ftmplt.search(template, text, "age")
(42, (33, 35))
The template object
If you're going to use the same pattern to match lots of strings you can use the
Template
object. Once initialised, the template object can be used similarly
to the functions above:
>>> import ftmplt
>>> template = ftmplt.Template("Hello, my name is {name} and I am {age:d} years old.")
>>> text = template.format(name="John", age=42)
>>> text
'Hello, my name is John and I am 42 years old.'
>>> template.parse(text)
{'name': 'John', 'age': 42}
>>> template.search("name", text)
('John', (19, 23))
Custom Format fields
You can define custom format fields by subclassing ftmplt.CustomFormatter
and implementing
the parse()
and format()
methods. For example, to parse and format a list of
integers, use the following formatter:
import ftmplt
class ArrayFormatter(ftmplt.CustomFormatter):
def parse(self, text: str):
return [int(v) for v in text.split(",")]
def format(self, value) -> str:
return ", ".join([str(v) for v in value])
The formatter has to be initialized with the key (name or index) of the format field:
>>> import ftmplt
>>> template = ftmplt.Template("The values {arr} are an array.", ArrayFormatter("arr"))
>>> text = template.format(arr=[1, 2, 3])
>>> text
'The values 1, 2, 3 are an array.'
>>> template.parse(text)
{'arr': [1, 2, 3]}
Example: Parsing a file
Let's say you have a file data.txt
with a bunch of parameters in it:
Input-File
N=50 M=100
X=1.0 Y=2.0 Z=3.0
Multiline text:
Some text
over multiple lines
You can handle the file formatting and parsing with a template:
import ftmplt
file = "data.txt"
template = ftmplt.Template("""
Input-File
N={n:d} M={m:d}
X={x:.1f} Y={y:.1f} Z={z:.f}
Multiline text:
{text}
""")
# Read file and parse data
data = template.parse_file(file)
# Update values
data["n"] = 100
...
# Update file contents
template.format_file(file, data)
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