Add str() builtin function

[certik]

Once LPython can use ASR's generic function facilities, it should just be a generic function. In the meantime, let's implement:

• str_int(x) ... converts an integer to a string
• str_float(x) ... converts a floating point to a string

These will be implemented in pure Python, such as:

def str_int(x):
 ....
 # s = ...
 return s

For now, let's put this into one file, and print the result at the end. Some things will not be implemented in LPython yet, so let's open up issues for things that are not implemented yet, and we'll fix them.

[Smit-create]

I tried implementing str_int(x) using different ways:

1. Using x: i32

Reference code

def str_int(x: i32) -> str:
 if x == 0:
 return '0'
 result: str
 result = ''
 if x < 0:
 result += '-'
 x = -x
 rev_result: str
 rev_result = ''
 pos_to_str: list
 pos_to_str = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']
 while x > 0:
 rev_result += pos_to_str[x%10]
 x = x//10
 for pos in range(len(rev_result) - 1, -1, -1):
 result += rev_result[pos]
 return result

AST

$ lfortran --show-python-ast --indent ser.txt
(Module [
 (FunctionDef 
 str_int 
 ([] [
 (
 x 
 (Name 
 i32 
 Load) ())] [] [] [] [] []) [
 (If 
 (Compare 
 (Name 
 x 
 Load) 
 Eq [
 (ConstantInt 0 ())]) [
 (Return 
 (ConstantStr "0" ()))] []) 
 (AnnAssign 
 (Name 
 result 
 Store) 
 (Name 
 str 
 Load) () 1) 
 (Assign [
 (Name 
 result 
 Store)] 
 (ConstantStr "" ()) ()) 
 (If 
 (Compare 
 (Name 
 x 
 Load) 
 Lt [
 (ConstantInt 0 ())]) [
 (AugAssign 
 (Name 
 result 
 Store) 
 Add 
 (ConstantStr "-" ())) 
 (Assign [
 (Name 
 x 
 Store)] 
 (UnaryOp 
 USub 
 (Name 
 x 
 Load)) ())] []) 
 (AnnAssign 
 (Name 
 rev_result 
 Store) 
 (Name 
 str 
 Load) () 1) 
 (Assign [
 (Name 
 rev_result 
 Store)] 
 (ConstantStr "" ()) ()) 
 (AnnAssign 
 (Name 
 pos_to_str 
 Store) 
 (Name 
 list 
 Load) () 1) 
 (Assign [
 (Name 
 pos_to_str 
 Store)] 
 (List [
 (ConstantStr "0" ()) 
 (ConstantStr "1" ()) 
 (ConstantStr "2" ()) 
 (ConstantStr "3" ()) 
 (ConstantStr "4" ()) 
 (ConstantStr "5" ()) 
 (ConstantStr "6" ()) 
 (ConstantStr "7" ()) 
 (ConstantStr "8" ()) 
 (ConstantStr "9" ())] 
 Load) ()) 
 (While 
 (Compare 
 (Name 
 x 
 Load) 
 Gt [
 (ConstantInt 0 ())]) [
 (AugAssign 
 (Name 
 rev_result 
 Store) 
 Add 
 (Subscript 
 (Name 
 pos_to_str 
 Load) 
 (BinOp 
 (Name 
 x 
 Load) 
 Mod 
 (ConstantInt 10 ())) 
 Load)) 
 (Assign [
 (Name 
 x 
 Store)] 
 (BinOp 
 (Name 
 x 
 Load) 
 FloorDiv 
 (ConstantInt 10 ())) ())] []) 
 (For 
 (Name 
 pos 
 Store) 
 (Call 
 (Name 
 range 
 Load) [
 (BinOp 
 (Call 
 (Name 
 len 
 Load) [
 (Name 
 rev_result 
 Load)] []) 
 Sub 
 (ConstantInt 1 ())) 
 (UnaryOp 
 USub 
 (ConstantInt 1 ())) 
 (UnaryOp 
 USub 
 (ConstantInt 1 ()))] []) [
 (AugAssign 
 (Name 
 result 
 Store) 
 Add 
 (Subscript 
 (Name 
 rev_result 
 Load) 
 (Name 
 pos 
 Load) 
 Load))] [] ()) 
 (Return 
 (Name 
 result 
 Load))] [] 
 (Name 
 str 
 Load) ())] [])

ASR

Traceback (most recent call last):
 Binary file "/home/admin-pc/Smitlunagariya/lfortran/inst/bin/lfortran", in _start()
 File "/build/glibc-S9d2JN/glibc-2.27/csu/../csu/libc-start.c", line 310, in __libc_start_main()
 File "/home/admin-pc/Smitlunagariya/lfortran/src/bin/lfortran.cpp", line 1504, in main()
 with_intrinsic_modules, compiler_options);
 File "/home/admin-pc/Smitlunagariya/lfortran/src/bin/lfortran.cpp", line 616, in emit_python_asr()
 r = LFortran::Python::python_ast_to_asr(al, *ast, diagnostics);
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/semantics/python_ast_to_asr.cpp", line 660, in LFortran::Python::python_ast_to_asr(Allocator&, LFortran::Python::AST::ast_t&, LFortran::diag::Diagnostics&)
 auto res2 = body_visitor(al, *ast_m, diagnostics, unit);
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/semantics/python_ast_to_asr.cpp", line 616, in LFortran::Python::body_visitor(Allocator&, LFortran::Python::AST::Module_t&, LFortran::diag::Diagnostics&, LFortran::ASR::asr_t*)
 b.visit_Module(ast);
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/semantics/python_ast_to_asr.cpp", line 299, in LFortran::Python::BodyVisitor::visit_Module(LFortran::Python::AST::Module_t const&)
 visit_stmt(*x.m_body[i]);
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/python_ast.h", line 1805, in LFortran::Python::AST::BaseVisitor<LFortran::Python::BodyVisitor>::visit_stmt(LFortran::Python::AST::stmt_t const&)
 void visit_stmt(const stmt_t &b) { visit_stmt_t(b, self()); }
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/python_ast.h", line 1677, in visit_stmt_t<LFortran::Python::BodyVisitor>()
 case stmtType::FunctionDef: { v.visit_FunctionDef((const FunctionDef_t &)x); return; }
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/semantics/python_ast_to_asr.cpp", line 312, in LFortran::Python::BodyVisitor::visit_FunctionDef(LFortran::Python::AST::FunctionDef_t const&)
 transform_stmts(body, x.n_body, x.m_body);
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/semantics/python_ast_to_asr.cpp", line 283, in LFortran::Python::BodyVisitor::transform_stmts(LFortran::Vec<LFortran::ASR::stmt_t*>&, unsigned long, LFortran::Python::AST::stmt_t**)
 this->visit_stmt(*m_body[i]);
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/python_ast.h", line 1805, in LFortran::Python::AST::BaseVisitor<LFortran::Python::BodyVisitor>::visit_stmt(LFortran::Python::AST::stmt_t const&)
 void visit_stmt(const stmt_t &b) { visit_stmt_t(b, self()); }
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/python_ast.h", line 1688, in visit_stmt_t<LFortran::Python::BodyVisitor>()
 case stmtType::If: { v.visit_If((const If_t &)x); return; }
LFortranException: visit_If() not implemented

2. Using str_int(x: int)

Reference code

 def str_int(x: int) -> str:
 if x == 0:
 return '0'
 result: str
 result = ''
 if x < 0:
 result += '-'
 x = -x
 rev_result: str
 rev_result = ''
 pos_to_str: list
 pos_to_str = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']
 while x > 0:
 rev_result += pos_to_str[x%10]
 x = x//10
 for pos in range(len(rev_result) - 1, -1, -1):
 result += rev_result[pos]
 return result

AST

(Module [
 (FunctionDef 
 str_int 
 ([] [
 (
 x 
 (Name 
 int 
 Load) ())] [] [] [] [] []) [
 (If 
 (Compare 
 (Name 
 x 
 Load) 
 Eq [
 (ConstantInt 0 ())]) [
 (Return 
 (ConstantStr "0" ()))] []) 
 (AnnAssign 
 (Name 
 result 
 Store) 
 (Name 
 str 
 Load) () 1) 
 (Assign [
 (Name 
 result 
 Store)] 
 (ConstantStr "" ()) ()) 
 (If 
 (Compare 
 (Name 
 x 
 Load) 
 Lt [
 (ConstantInt 0 ())]) [
 (AugAssign 
 (Name 
 result 
 Store) 
 Add 
 (ConstantStr "-" ())) 
 (Assign [
 (Name 
 x 
 Store)] 
 (UnaryOp 
 USub 
 (Name 
 x 
 Load)) ())] []) 
 (AnnAssign 
 (Name 
 rev_result 
 Store) 
 (Name 
 str 
 Load) () 1) 
 (Assign [
 (Name 
 rev_result 
 Store)] 
 (ConstantStr "" ()) ()) 
 (AnnAssign 
 (Name 
 pos_to_str 
 Store) 
 (Name 
 list 
 Load) () 1) 
 (Assign [
 (Name 
 pos_to_str 
 Store)] 
 (List [
 (ConstantStr "0" ()) 
 (ConstantStr "1" ()) 
 (ConstantStr "2" ()) 
 (ConstantStr "3" ()) 
 (ConstantStr "4" ()) 
 (ConstantStr "5" ()) 
 (ConstantStr "6" ()) 
 (ConstantStr "7" ()) 
 (ConstantStr "8" ()) 
 (ConstantStr "9" ())] 
 Load) ()) 
 (While 
 (Compare 
 (Name 
 x 
 Load) 
 Gt [
 (ConstantInt 0 ())]) [
 (AugAssign 
 (Name 
 rev_result 
 Store) 
 Add 
 (Subscript 
 (Name 
 pos_to_str 
 Load) 
 (BinOp 
 (Name 
 x 
 Load) 
 Mod 
 (ConstantInt 10 ())) 
 Load)) 
 (Assign [
 (Name 
 x 
 Store)] 
 (BinOp 
 (Name 
 x 
 Load) 
 FloorDiv 
 (ConstantInt 10 ())) ())] []) 
 (For 
 (Name 
 pos 
 Store) 
 (Call 
 (Name 
 range 
 Load) [
 (BinOp 
 (Call 
 (Name 
 len 
 Load) [
 (Name 
 rev_result 
 Load)] []) 
 Sub 
 (ConstantInt 1 ())) 
 (UnaryOp 
 USub 
 (ConstantInt 1 ())) 
 (UnaryOp 
 USub 
 (ConstantInt 1 ()))] []) [
 (AugAssign 
 (Name 
 result 
 Store) 
 Add 
 (Subscript 
 (Name 
 rev_result 
 Load) 
 (Name 
 pos 
 Load) 
 Load))] [] ()) 
 (Return 
 (Name 
 result 
 Load))] [] 
 (Name 
 str 
 Load) ())] [])

ASR

semantic error: Annotation type not supported
 --> ser.txt:1:1
 |
1 | 0 0 1 0 7 str_int 0 1 1 x 1 26 3 int 0 0 0 0 0 0 0 11 11 15 26 1 x 0 0 1 20 0 0 1 3 1 19 1 0 0 0 7 26 6 result 1 26 3 str 0 0 1 5 1 26 6 result 1 19 0 0 0 11 15 26 1 x 0 2 1 20 0 0 2 6 26 6 result 1 0 19 1 - 0 5 1 26 1 x 1 3 3 26 1 x 0 0 0 7 26 10 rev_result 1 26 3 str 0 0 1 5 1 26 10 rev_result 1 19 0 0 0 7 26 10 pos_to_str 1 26 4 list 0 0 1 5 1 26 10 pos_to_str 1 27 10 19 1 0 0 19 1 1 0 19 1 2 0 19 1 3 0 19 1 4 0 19 1 5 0 19 1 6 0 19 1 7 0 19 1 8 0 19 1 9 0 0 0 10 15 26 1 x 0 4 1 20 0 0 2 6 26 10 rev_result 1 0 24 26 10 pos_to_str 0 2 26 1 x 0 5 20 10 0 0 5 1 26 1 x 1 2 26 1 x 0 12 20 10 0 0 0 8 26 3 pos 1 16 26 5 range 0 3 2 16 26 3 len 0 1 26 10 rev_result 0 0 1 20 1 0 3 3 20 1 0 3 3 20 1 0 0 1 6 26 6 result 1 0 24 26 10 rev_result 0 26 3 pos 0 0 0 0 3 1 26 6 result 0 0 1 26 3 str 0 0 0 
 | ^ 


Note: if any of the above error or warning messages are not clear or are lacking
context please report it to us (we consider that a bug that needs to be fixed).

3. Using the magic method (__str__)

Reference code

def str_int(x: i32) -> str:
 return x.__str__()

AST

(Module [
 (FunctionDef 
 str_int 
 ([] [
 (
 x 
 (Name 
 i32 
 Load) ())] [] [] [] [] []) [
 (Return 
 (Call 
 (Attribute 
 (Name 
 x 
 Load) 
 __str__ 
 Load) [] []))] [] 
 (Name 
 str 
 Load) ())] [])

ASR

Traceback (most recent call last):
 Binary file "/home/admin-pc/Smitlunagariya/lfortran/inst/bin/lfortran", in _start()
 File "/build/glibc-S9d2JN/glibc-2.27/csu/../csu/libc-start.c", line 310, in __libc_start_main()
 File "/home/admin-pc/Smitlunagariya/lfortran/src/bin/lfortran.cpp", line 1504, in main()
 with_intrinsic_modules, compiler_options);
 File "/home/admin-pc/Smitlunagariya/lfortran/src/bin/lfortran.cpp", line 616, in emit_python_asr()
 r = LFortran::Python::python_ast_to_asr(al, *ast, diagnostics);
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/semantics/python_ast_to_asr.cpp", line 660, in LFortran::Python::python_ast_to_asr(Allocator&, LFortran::Python::AST::ast_t&, LFortran::diag::Diagnostics&)
 auto res2 = body_visitor(al, *ast_m, diagnostics, unit);
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/semantics/python_ast_to_asr.cpp", line 616, in LFortran::Python::body_visitor(Allocator&, LFortran::Python::AST::Module_t&, LFortran::diag::Diagnostics&, LFortran::ASR::asr_t*)
 b.visit_Module(ast);
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/semantics/python_ast_to_asr.cpp", line 299, in LFortran::Python::BodyVisitor::visit_Module(LFortran::Python::AST::Module_t const&)
 visit_stmt(*x.m_body[i]);
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/python_ast.h", line 1805, in LFortran::Python::AST::BaseVisitor<LFortran::Python::BodyVisitor>::visit_stmt(LFortran::Python::AST::stmt_t const&)
 void visit_stmt(const stmt_t &b) { visit_stmt_t(b, self()); }
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/python_ast.h", line 1677, in visit_stmt_t<LFortran::Python::BodyVisitor>()
 case stmtType::FunctionDef: { v.visit_FunctionDef((const FunctionDef_t &)x); return; }
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/semantics/python_ast_to_asr.cpp", line 312, in LFortran::Python::BodyVisitor::visit_FunctionDef(LFortran::Python::AST::FunctionDef_t const&)
 transform_stmts(body, x.n_body, x.m_body);
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/semantics/python_ast_to_asr.cpp", line 283, in LFortran::Python::BodyVisitor::transform_stmts(LFortran::Vec<LFortran::ASR::stmt_t*>&, unsigned long, LFortran::Python::AST::stmt_t**)
 this->visit_stmt(*m_body[i]);
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/python_ast.h", line 1805, in LFortran::Python::AST::BaseVisitor<LFortran::Python::BodyVisitor>::visit_stmt(LFortran::Python::AST::stmt_t const&)
 void visit_stmt(const stmt_t &b) { visit_stmt_t(b, self()); }
 File "/home/admin-pc/Smitlunagariya/lfortran/src/lfortran/python_ast.h", line 1680, in visit_stmt_t<LFortran::Python::BodyVisitor>()
 case stmtType::Return: { v.visit_Return((const Return_t &)x); return; }
LFortranException: visit_Return() not implemented

[certik]

Perfect, thanks. Yes, we have to implement if and return. For pos_to_str = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'], we'll probably implement it as a 1D array.

[Smit-create]

Well, float_to_string requires float_to_int and we may have to set the precision too. builtin magic method __str__ might be best option for str_float.

[certik]

Let's use chr(ord('0')+i) instead of ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'][i].

[certik]

Let's implement chr and ord like this:

# Uncomment once we implement the `sys` module
#from sys import exit

def ord(s: str) -> i32:
 if s == '0':
 return 48
 elif s == '1':
 return 49
 else:
 exit(1)

def chr(i: i32) -> str:
 if i == 48:
 return '0'
 elif i == 49:
 return '1'
 else:
 exit(1)

[certik]

To implement some of the features that we need, isolate the given feature and try to implement it, such as:

def test1():
 result: str
 result = "a"
 result += "x"

[ubaidsk]

Let's implement chr and ord like this:

# Uncomment once we implement the `sys` module
#from sys import exit

def ord(s: str) -> i32:
 if s == '0':
 return 48
 elif s == '1':
 return 49
 else:
 exit(1)

def chr(i: i32) -> str:
 if i == 48:
 return '0'
 elif i == 49:
 return '1'
 else:
 exit(1)

The ord and chr functions fail if characters other than '0', '1' for ord and unicode values other than 48, 49 for chr are passed. How are we planning to deal with this?

[ubaidsk]

Shall I update the functions ord and chr as follows:

def ord(s: str) -> i32: # supports characters with unicode value between 32 to 126
 if len(s) != 1:
 return "Not a Character"
 for i in range(32, 127):
 if chr(i) == s:
 return i
 

def chr(i: i32) -> str: # supports unicode values between 32 to 126
 if i < 32 or i > 126:
 return "Not Yet Supported"
 all_chars = ' !"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~'
 return all_chars[i - 32]

Testing Code:

testing_chars = ' !"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~'
for ch in testing_chars:
 print(f"{ch}: {ord(ch)}")

Testing Code Output:

 : 32
!: 33
": 34
#: 35
$: 36
%: 37
&: 38
': 39
(: 40
): 41
*: 42
+: 43
,: 44
-: 45
.: 46
/: 47
0: 48
1: 49
2: 50
3: 51
4: 52
5: 53
6: 54
7: 55
8: 56
9: 57
:: 58
;: 59
<: 60
=: 61
>: 62
?: 63
@: 64
A: 65
B: 66
C: 67
D: 68
E: 69
F: 70
G: 71
H: 72
I: 73
J: 74
K: 75
L: 76
M: 77
N: 78
O: 79
P: 80
Q: 81
R: 82
S: 83
T: 84
U: 85
V: 86
W: 87
X: 88
Y: 89
Z: 90
[: 91
\: 92
]: 93
^: 94
_: 95
`: 96
a: 97
b: 98
c: 99
d: 100
e: 101
f: 102
g: 103
h: 104
i: 105
j: 106
k: 107
l: 108
m: 109
n: 110
o: 111
p: 112
q: 113
r: 114
s: 115
t: 116
u: 117
v: 118
w: 119
x: 120
y: 121
z: 122
{: 123
|: 124
}: 125
~: 126

To accomplish #281 , I think that we might need ord and chr functions to implement string methods like isalpha, isupper, etc.

[certik]

@Shaikh-Ubaid I think so. I think we might need to fix some bugs in LPython to make it work, but I think an implementation along your lines should work. Can you please submit it as a PR and add some tests?

P.S. My apologies for late answer, I just noticed your comments now.

[ubaidsk]

Can you please submit it as a PR and add some tests?

Yes, I will submit the ord and chr implementations along with integrations tests.