feature:minor

1. Added count function for strings str.count().

Author: SudhanshuJoshi09

src/lpython/semantics/python_ast_to_asr.cpp

@@ -6791,6 +6791,28 @@ class BodyVisitor : public CommonVisitor<BodyVisitor> {
                 [&](const std::string &msg, const Location &loc) {
                 throw SemanticError(msg, loc); });
             return;
+        } else if(attr_name == "count") {
+            if(args.size() != 1) {
+                throw SemanticError("str.count() takes one argument for now.", loc);
+            }
+            ASR::expr_t *arg_value = args[0].m_value;
+            ASR::ttype_t *arg_value_type = ASRUtils::expr_type(arg_value);
+            if (!ASRUtils::is_character(*arg_value_type)) {
+                throw SemanticError("str.count() takes one argument of type: str", loc);
+            }
+
+            fn_call_name = "_lpython_str_count";
+            ASR::call_arg_t str;
+            str.loc = loc;
+            str.m_value = s_var;
+
+            ASR::call_arg_t value;
+            value.loc = loc;
+            value.m_value = args[0].m_value;
+
+            // Push string and substring argument on top of Vector (or Function Arguments Stack basically)
+            fn_args.push_back(al, str);
+            fn_args.push_back(al, value);
         } else if(attr_name.size() > 2 && attr_name[0] == 'i' && attr_name[1] == 's') {
             /*
                 String Validation Methods i.e all "is" based functions are handled here

src/lpython/semantics/python_comptime_eval.h

@@ -77,6 +77,7 @@ struct PythonIntrinsicProcedures {
             // The following functions for string methods are not used
             // for evaluation.
             {"_lpython_str_capitalize", {m_builtin, &not_implemented}},
+            {"_lpython_str_count", {m_builtin, &not_implemented}},
             {"_lpython_str_lower", {m_builtin, &not_implemented}},
             {"_lpython_str_upper", {m_builtin, &not_implemented}},
             {"_lpython_str_find", {m_builtin, &not_implemented}},

src/runtime/lpython_builtin.py

@@ -722,6 +722,22 @@ def _lpython_str_capitalize(x: str) -> str:
     res = chr(val) + res[1:]
     return res
 
+
+@overload
+def _lpython_str_count(x: str, y: str) -> i32:
+    assert (len(y) == 0), 'The length y should one for now.'
+
+    count : i32
+    count = 0
+
+    i: str
+
+    for i in x:
+        count += i32(i == y)
+
+    return count
+
+
 @overload
 def _lpython_str_lower(x: str) -> str:
     res: str