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Feature: str.format accepting !r, !s and !a #1027

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Merged
merged 4 commits into from
Jun 10, 2019
Merged

Feature: str.format accepting !r, !s and !a #1027

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65d0093
Dont fail on '{!r}'.format(...)
alanjds Jun 9, 2019
e19b674
FormatSpec got a preconversor:FormatPreconversor to handle !r, !s and !a
alanjds Jun 9, 2019
f0a2b4c
Apply the {!r} on str.format calls
alanjds Jun 9, 2019
854bacf
Fix the Rust tests
alanjds Jun 9, 2019
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21 changes: 19 additions & 2 deletions tests/snippets/strings.py
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Original file line number Diff line number Diff line change
Expand Up @@ -182,10 +182,27 @@
assert not '123'.isidentifier()

# String Formatting
assert "{} {}".format(1,2) == "1 2"
assert "{0} {1}".format(2,3) == "2 3"
assert "{} {}".format(1, 2) == "1 2"
assert "{0} {1}".format(2, 3) == "2 3"
assert "--{:s>4}--".format(1) == "--sss1--"
assert "{keyword} {0}".format(1, keyword=2) == "2 1"
assert "repr() shows quotes: {!r}; str() doesn't: {!s}".format(
'test1', 'test2'
) == "repr() shows quotes: 'test1'; str() doesn't: test2", 'Output: {!r}, {!s}'.format('test1', 'test2')


class Foo:
def __str__(self):
return 'str(Foo)'

def __repr__(self):
return 'repr(Foo)'


f = Foo()
assert "{} {!s} {!r} {!a}".format(f, f, f, f) == 'str(Foo) str(Foo) repr(Foo) repr(Foo)'
assert "{foo} {foo!s} {foo!r} {foo!a}".format(foo=f) == 'str(Foo) str(Foo) repr(Foo) repr(Foo)'
# assert '{} {!r} {:10} {!r:10} {foo!r:10} {foo!r} {foo}'.format('txt1', 'txt2', 'txt3', 'txt4', 'txt5', foo='bar')

assert 'a' < 'b'
assert 'a' <= 'b'
Expand Down
67 changes: 66 additions & 1 deletion vm/src/format.rs
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Expand Up @@ -3,6 +3,49 @@ use num_traits::Signed;
use std::cmp;
use std::str::FromStr;

#[derive(Debug, Copy, Clone, PartialEq)]
pub enum FormatPreconversor {
Str,
Repr,
Ascii,
}

impl FormatPreconversor {
pub fn from_char(c: char) -> Option<FormatPreconversor> {
match c {
's' => Some(FormatPreconversor::Str),
'r' => Some(FormatPreconversor::Repr),
'a' => Some(FormatPreconversor::Ascii),
_ => None,
}
}

pub fn from_str(text: &str) -> Option<FormatPreconversor> {
let mut chars = text.chars();
if chars.next() != Some('!') {
return None;
}

match chars.next() {
None => None, // Should fail instead?
Some(c) => FormatPreconversor::from_char(c),
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This can just be chars.next().map(FormatPreconversor::from_char)

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Hum... this still returns None if chars.next() is None?

Asking because FormatPreconversor::from_char is not prepared to handle None as input.

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Another aspect: // Should fail instead?

I do not know how to raise exceptions. Ideally, {!x} should fail, but this code will pass for now:

# CPy 3.6
>>> '{!x}'.format(123)
Traceback (most recent call last):
  File "<ipython-input-2-b294f18f6498>", line 1, in <module>
    '{!x}'.format(123)
ValueError: Unknown conversion specifier x
# RustPython
>>>>> '{!x}'.format(123)
'123'

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@silmeth silmeth Jun 11, 2019 •
edited
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next().map(FormatPreconversor::from_char) would just map the inner value of the Option if present – would do exactly what you did (pass the inner value to from_char() if it exists, or return None if the Option is None).

To raise an exception, you’d need to signal an error somehow (eg. return a Result<Option<FormatPreconversor>, String> instead of an Option<FormatPreconversor>) and then check for the result in call_object_format() and in case of an error, return a new vm error there (eg. by return Err(vm.new_value_error(…))). Or just by mapping the error:

let (preconversor, new_format_spec) = FormatPreconversor::parse_and_consume(format_spec);
let preconversor = preconversor.map_err(|msg| vm.new_value_error(msg))?;
// …

But then you’d probably want to return Result<(Option<FormatPreconversor>, &str), String> rather than (Result<Option<FormatPreconversor>, String>, &str), so that it’d look like:

let (preconversor, new_format_spec) = FormatPreconversor::parse_and_consume(format_spec)
    .map_err(|msg| vm.new_value_error(msg))?;

See https://doc.rust-lang.org/std/result/

}
}

pub fn parse_and_consume(text: &str) -> (Option<FormatPreconversor>, &str) {
let preconversor = FormatPreconversor::from_str(text);
match preconversor {
None => (None, text),
Some(_) => {
let mut chars = text.chars();
chars.next(); // Consume the bang
chars.next(); // Consume one r,s,a char
(preconversor, chars.as_str())
}
}
}
}

#[derive(Debug, Copy, Clone, PartialEq)]
pub enum FormatAlign {
Left,
Expand Down Expand Up @@ -56,6 +99,7 @@ pub enum FormatType {

#[derive(Debug, PartialEq)]
pub struct FormatSpec {
preconversor: Option<FormatPreconversor>,
fill: Option<char>,
align: Option<FormatAlign>,
sign: Option<FormatSign>,
Expand All @@ -75,6 +119,10 @@ fn get_num_digits(text: &str) -> usize {
text.len()
}

fn parse_preconversor(text: &str) -> (Option<FormatPreconversor>, &str) {
FormatPreconversor::parse_and_consume(text)
}

fn parse_align(text: &str) -> (Option<FormatAlign>, &str) {
let mut chars = text.chars();
let maybe_align = chars.next().and_then(FormatAlign::from_char);
Expand Down Expand Up @@ -186,7 +234,8 @@ fn parse_format_type(text: &str) -> (Option<FormatType>, &str) {
}

fn parse_format_spec(text: &str) -> FormatSpec {
let (fill, align, after_align) = parse_fill_and_align(text);
let (preconversor, after_preconversor) = parse_preconversor(text);
let (fill, align, after_align) = parse_fill_and_align(after_preconversor);
let (sign, after_sign) = parse_sign(after_align);
let (alternate_form, after_alternate_form) = parse_alternate_form(after_sign);
let after_zero = parse_zero(after_alternate_form);
Expand All @@ -196,6 +245,7 @@ fn parse_format_spec(text: &str) -> FormatSpec {
let (format_type, _) = parse_format_type(after_precision);

FormatSpec {
preconversor,
fill,
align,
sign,
Expand Down Expand Up @@ -467,6 +517,18 @@ impl FormatString {
String::new()
};

// On parts[0] can still be the preconversor (!r, !s, !a)
let parts: Vec<&str> = arg_part.splitn(2, '!').collect();
// before the bang is a keyword or arg index, after the comma is maybe a conversor spec.
let arg_part = parts[0];

let preconversor_spec = if parts.len() > 1 {
"!".to_string() + parts[1]
} else {
String::new()
};
let format_spec = preconversor_spec + &format_spec;

if arg_part.is_empty() {
return Ok(FormatPart::AutoSpec(format_spec));
}
Expand Down Expand Up @@ -551,6 +613,7 @@ mod tests {
#[test]
fn test_width_only() {
let expected = FormatSpec {
preconversor: None,
fill: None,
align: None,
sign: None,
Expand All @@ -566,6 +629,7 @@ mod tests {
#[test]
fn test_fill_and_width() {
let expected = FormatSpec {
preconversor: None,
fill: Some('<'),
align: Some(FormatAlign::Right),
sign: None,
Expand All @@ -581,6 +645,7 @@ mod tests {
#[test]
fn test_all() {
let expected = FormatSpec {
preconversor: None,
fill: Some('<'),
align: Some(FormatAlign::Right),
sign: Some(FormatSign::Minus),
Expand Down
12 changes: 10 additions & 2 deletions vm/src/obj/objstr.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ use unicode_casing::CharExt;
use unicode_segmentation::UnicodeSegmentation;
use unicode_xid::UnicodeXID;

use crate::format::{FormatParseError, FormatPart, FormatString};
use crate::format::{FormatParseError, FormatPart, FormatPreconversor, FormatString};
use crate::function::{single_or_tuple_any, OptionalArg, PyFuncArgs};
use crate::pyhash;
use crate::pyobject::{
Expand Down Expand Up @@ -1026,7 +1026,15 @@ fn count_char(s: &str, c: char) -> usize {
}

fn call_object_format(vm: &VirtualMachine, argument: PyObjectRef, format_spec: &str) -> PyResult {
let returned_type = vm.ctx.new_str(format_spec.to_string());
let (preconversor, new_format_spec) = FormatPreconversor::parse_and_consume(format_spec);
let argument = match preconversor {
Some(FormatPreconversor::Str) => vm.call_method(&argument, "__str__", vec![])?,
Some(FormatPreconversor::Repr) => vm.call_method(&argument, "__repr__", vec![])?,
Some(FormatPreconversor::Ascii) => vm.call_method(&argument, "__repr__", vec![])?,
None => argument,
};
let returned_type = vm.ctx.new_str(new_format_spec.to_string());

let result = vm.call_method(&argument, "__format__", vec![returned_type])?;
if !objtype::isinstance(&result, &vm.ctx.str_type()) {
let result_type = result.class();
Expand Down