⚡️ Speed up function do_for by 46%

[codeflash-ai]

📄 46% (0.46x) speedup for do_for in django/template/defaulttags.py

⏱️ Runtime : 1.12 milliseconds → 767 microseconds (best of 46 runs)

📝 Explanation and details

Key optimizations made:

• Avoided regex (re.split) for comma splitting loopvars, as this was responsible for ~27.9% of runtime and is unnecessary for simple cases.
• Only use fast str.split(',') and str.strip() instead of regex. This greatly reduces the cost for the common case (single variable or simple comma-separated variables), lowering memory use and CPU cycles.
• Preserved all error checking and behavior exactly.
• Preserved all comments and docstring as in original.
• Retained all type usage, control flow, and original code style.

This approach is both safe and performance improved, especially for templates that have simple or typical variable unpacking cases. Regex engine overhead is avoided entirely unless Django's complex template parsing actually demands it (which is not the case for comma separation).

✅ Correctness verification report:

Test	Status
⚙️ Existing Unit Tests	🔘 None Found
🌀 Generated Regression Tests	✅ 27 Passed
⏪ Replay Tests	🔘 None Found
🔎 Concolic Coverage Tests	🔘 None Found
📊 Tests Coverage	100.0%

🌀 Generated Regression Tests and Runtime

import re

# imports
import pytest
from django.template.defaulttags import do_for


# Mocks and stubs for the Django template system
class DummyToken:
    def __init__(self, contents):
        self.contents = contents

    def split_contents(self):
        # Simulate Django's Token.split_contents()
        return self.contents.split()

class DummyParser:
    def __init__(self, filters=None, tokens=None):
        self.filters = filters or {}
        self.tokens = tokens or []
        self.token_index = 0
        self.parsed_tags = []
        self.deleted_tokens = []
        self.parse_calls = []

    def compile_filter(self, expr):
        # Simulate Django's compile_filter (returns the expr for test)
        self.filters.setdefault(expr, expr)
        return expr

    def parse(self, stop_tags):
        # Simulate parsing until a stop tag is found.
        self.parse_calls.append(stop_tags)
        # Return a dummy nodelist depending on stop_tags
        # For test, just return stop_tags as the nodelist
        self.parsed_tags.append(stop_tags)
        return ["nodelist_" + "_".join(stop_tags)]

    def next_token(self):
        # Simulate getting the next token from the token stream
        if self.token_index < len(self.tokens):
            tok = self.tokens[self.token_index]
            self.token_index += 1
            return DummyToken(tok)
        # If no more tokens, return a dummy endfor token
        return DummyToken("endfor")

    def delete_first_token(self):
        # Simulate deleting the first token
        self.deleted_tokens.append("deleted")

# Minimal TemplateSyntaxError for testing
class TemplateSyntaxError(Exception):
    pass

# Minimal ForNode for testing
class ForNode:
    def __init__(self, loopvars, sequence, is_reversed, nodelist_loop, nodelist_empty):
        self.loopvars = loopvars
        self.sequence = sequence
        self.is_reversed = is_reversed
        self.nodelist_loop = nodelist_loop
        self.nodelist_empty = nodelist_empty

# FILTER_SEPARATOR for validation
FILTER_SEPARATOR = '|'
from django.template.defaulttags import do_for

# =========================
# Unit Tests for do_for
# =========================

# ----------- Basic Test Cases -----------
def test_basic_single_loopvar():
    # Test a basic for loop: {% for x in arr %}
    parser = DummyParser()
    token = DummyToken("for x in arr")
    codeflash_output = do_for(parser, token); node = codeflash_output # 6.89μs -> 4.96μs (39.0% faster)

def test_basic_multiple_loopvars():
    # Test a for loop with unpacking: {% for key, value in dict.items %}
    parser = DummyParser()
    token = DummyToken("for key, value in dict.items")
    codeflash_output = do_for(parser, token); node = codeflash_output # 7.31μs -> 5.72μs (27.9% faster)

def test_basic_reversed():
    # Test a for loop with reversed: {% for x in arr reversed %}
    parser = DummyParser()
    token = DummyToken("for x in arr reversed")
    codeflash_output = do_for(parser, token); node = codeflash_output # 6.01μs -> 4.60μs (30.7% faster)

def test_basic_with_empty_clause():
    # Test a for loop with empty clause: {% for x in arr %} ... {% empty %} ... {% endfor %}
    parser = DummyParser(tokens=["empty", "endfor"])
    token = DummyToken("for x in arr")
    codeflash_output = do_for(parser, token); node = codeflash_output # 6.74μs -> 4.88μs (37.9% faster)

# ----------- Edge Test Cases -----------







def test_edge_empty_clause_no_endfor():
    # Should still work if empty clause is present and endfor is next
    parser = DummyParser(tokens=["empty", "endfor"])
    token = DummyToken("for x in arr")
    codeflash_output = do_for(parser, token); node = codeflash_output # 8.95μs -> 6.36μs (40.7% faster)

def test_edge_reversed_with_unpacking():
    # Test reversed with multiple loopvars
    parser = DummyParser()
    token = DummyToken("for key, value in dict.items reversed")
    codeflash_output = do_for(parser, token); node = codeflash_output # 8.52μs -> 6.60μs (29.0% faster)

def test_edge_extra_spaces_in_loopvars():
    # Test loopvars with extra spaces between commas
    parser = DummyParser()
    token = DummyToken("for key , value in dict.items")
    codeflash_output = do_for(parser, token); node = codeflash_output # 7.82μs -> 6.19μs (26.4% faster)

# ----------- Large Scale Test Cases -----------

def test_large_scale_many_loopvars():
    # Test with a large number of loopvars (up to 1000)
    loopvars = [f"var{i}" for i in range(1000)]
    loopvars_str = ", ".join(loopvars)
    parser = DummyParser()
    token = DummyToken(f"for {loopvars_str} in biglist")
    codeflash_output = do_for(parser, token); node = codeflash_output # 247μs -> 167μs (47.9% faster)

def test_large_scale_long_sequence_name():
    # Test with a long sequence name
    seq_name = "a" * 500
    parser = DummyParser()
    token = DummyToken(f"for x in {seq_name}")
    codeflash_output = do_for(parser, token); node = codeflash_output # 6.85μs -> 5.11μs (34.0% faster)

def test_large_scale_many_tokens():
    # Simulate a parser with many tokens for empty clause
    tokens = ["empty"] + ["endfor"] * 999
    parser = DummyParser(tokens=tokens)
    token = DummyToken("for x in arr")
    codeflash_output = do_for(parser, token); node = codeflash_output # 6.74μs -> 4.85μs (38.9% faster)

def test_large_scale_multiple_parse_calls():
    # Ensure parser.parse is called with correct stop tags even for large scale
    parser = DummyParser(tokens=["empty", "endfor"])
    token = DummyToken("for x in arr")
    do_for(parser, token) # 6.05μs -> 4.84μs (25.1% faster)

def test_large_scale_performance():
    # Test performance: do_for should not hang or be slow with large input
    loopvars = [f"v{i}" for i in range(999)]
    loopvars_str = ", ".join(loopvars)
    parser = DummyParser()
    token = DummyToken(f"for {loopvars_str} in biglist reversed")
    codeflash_output = do_for(parser, token); node = codeflash_output # 212μs -> 143μs (47.8% faster)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.
#------------------------------------------------
import re

# imports
import pytest
from django.template.defaulttags import do_for


# Mocks and helpers for testing do_for
class DummyToken:
    """A dummy token class to simulate Django's token."""
    def __init__(self, contents):
        self.contents = contents

    def split_contents(self):
        return self.contents.split()

class DummyParser:
    """A dummy parser class to simulate Django's parser behavior."""
    def __init__(self, tokens_to_parse=None, next_token_contents=None):
        self._tokens_to_parse = tokens_to_parse or []
        self._next_token_contents = next_token_contents
        self._parse_calls = []
        self._next_token_called = False
        self._delete_first_token_called = False

    def compile_filter(self, expr):
        # For testing, just return the expression string
        return expr

    def parse(self, stop_tokens):
        # Return a string indicating what was parsed
        self._parse_calls.append(stop_tokens)
        return f"nodelist_{'_'.join(stop_tokens)}"

    def next_token(self):
        self._next_token_called = True
        return DummyToken(self._next_token_contents)

    def delete_first_token(self):
        self._delete_first_token_called = True

class ForNode:
    """A dummy ForNode to simulate Django's ForNode."""
    def __init__(self, loopvars, sequence, is_reversed, nodelist_loop, nodelist_empty):
        self.loopvars = loopvars
        self.sequence = sequence
        self.is_reversed = is_reversed
        self.nodelist_loop = nodelist_loop
        self.nodelist_empty = nodelist_empty

# Minimal TemplateSyntaxError for testing
class TemplateSyntaxError(Exception):
    pass

# FILTER_SEPARATOR for testing
FILTER_SEPARATOR = '|'
from django.template.defaulttags import do_for

# unit tests

# ---------------- Basic Test Cases ----------------

def test_for_single_variable_basic():
    """Test a basic for loop with a single variable."""
    parser = DummyParser(next_token_contents="endfor")
    token = DummyToken("for athlete in athlete_list")
    codeflash_output = do_for(parser, token); node = codeflash_output # 6.70μs -> 4.91μs (36.6% faster)

def test_for_multiple_variables_basic():
    """Test a for loop with multiple variables unpacked."""
    parser = DummyParser(next_token_contents="endfor")
    token = DummyToken("for key, value in dict.items")
    codeflash_output = do_for(parser, token); node = codeflash_output # 6.92μs -> 5.24μs (32.0% faster)

def test_for_single_variable_reversed():
    """Test a for loop with a single variable and reversed."""
    parser = DummyParser(next_token_contents="endfor")
    token = DummyToken("for athlete in athlete_list reversed")
    codeflash_output = do_for(parser, token); node = codeflash_output # 6.05μs -> 4.36μs (39.0% faster)

def test_for_with_empty_clause():
    """Test a for loop with an empty clause."""
    parser = DummyParser(next_token_contents="empty")
    token = DummyToken("for athlete in athlete_list")
    codeflash_output = do_for(parser, token); node = codeflash_output # 6.20μs -> 4.50μs (37.8% faster)

# ---------------- Edge Test Cases ----------------







def test_for_multiple_loopvars_with_spaces():
    """Test that multiple loopvars separated by comma but with spaces are parsed correctly."""
    parser = DummyParser(next_token_contents="endfor")
    token = DummyToken("for key , value in dict.items")
    codeflash_output = do_for(parser, token); node = codeflash_output # 9.81μs -> 7.55μs (30.0% faster)

def test_for_with_extra_spaces():
    """Test that extra spaces between loopvars and commas are handled."""
    parser = DummyParser(next_token_contents="endfor")
    token = DummyToken("for key   ,   value in dict.items")
    codeflash_output = do_for(parser, token); node = codeflash_output # 7.61μs -> 5.79μs (31.5% faster)

def test_for_with_reversed_and_empty_clause():
    """Test for loop with reversed and empty clause."""
    parser = DummyParser(next_token_contents="empty")
    token = DummyToken("for athlete in athlete_list reversed")
    codeflash_output = do_for(parser, token); node = codeflash_output # 7.06μs -> 5.21μs (35.5% faster)

# ---------------- Large Scale Test Cases ----------------

def test_for_large_number_of_loopvars():
    """Test for loop with a large number of loopvars (up to 1000)."""
    loopvars = [f'var{i}' for i in range(1000)]
    loopvar_str = ', '.join(loopvars)
    parser = DummyParser(next_token_contents="endfor")
    token = DummyToken(f"for {loopvar_str} in big_list")
    codeflash_output = do_for(parser, token); node = codeflash_output # 248μs -> 167μs (48.4% faster)

def test_for_large_sequence_name():
    """Test for loop with a very large sequence name."""
    seq_name = 'a' * 1000
    parser = DummyParser(next_token_contents="endfor")
    token = DummyToken(f"for athlete in {seq_name}")
    codeflash_output = do_for(parser, token); node = codeflash_output # 6.91μs -> 5.09μs (35.7% faster)

def test_for_loopvars_with_long_names():
    """Test for loop with loopvars having very long names."""
    loopvars = ['x' * 250, 'y' * 250]
    loopvar_str = ', '.join(loopvars)
    parser = DummyParser(next_token_contents="endfor")
    token = DummyToken(f"for {loopvar_str} in dict.items")
    codeflash_output = do_for(parser, token); node = codeflash_output # 13.9μs -> 8.67μs (59.9% faster)

def test_for_reversed_large_scale():
    """Test for loop with reversed and large scale loopvars."""
    loopvars = [f'var{i}' for i in range(999)]
    loopvar_str = ', '.join(loopvars)
    parser = DummyParser(next_token_contents="endfor")
    token = DummyToken(f"for {loopvar_str} in big_list reversed")
    codeflash_output = do_for(parser, token); node = codeflash_output # 241μs -> 163μs (48.0% faster)

# ---------------- Additional Edge Cases ----------------

def test_for_loopvars_with_leading_trailing_spaces():
    """Test loopvars with leading/trailing spaces (should be stripped by split)."""
    parser = DummyParser(next_token_contents="endfor")
    token = DummyToken("for   athlete   in athlete_list")
    codeflash_output = do_for(parser, token); node = codeflash_output # 5.96μs -> 4.52μs (31.8% faster)

def test_for_loopvars_with_multiple_commas_and_spaces():
    """Test loopvars with multiple commas and spaces."""
    parser = DummyParser(next_token_contents="endfor")
    token = DummyToken("for key  ,  value  ,  index in dict.items")
    codeflash_output = do_for(parser, token); node = codeflash_output # 7.28μs -> 6.07μs (19.8% faster)

def test_for_with_empty_clause_and_no_loop_content():
    """Test for loop with empty clause and no loop content."""
    parser = DummyParser(next_token_contents="empty")
    token = DummyToken("for athlete in athlete_list")
    codeflash_output = do_for(parser, token); node = codeflash_output # 6.41μs -> 4.51μs (42.0% faster)

def test_for_with_reversed_and_large_sequence_name():
    """Test for loop with reversed and very large sequence name."""
    seq_name = 'b' * 999
    parser = DummyParser(next_token_contents="endfor")
    token = DummyToken(f"for athlete in {seq_name} reversed")
    codeflash_output = do_for(parser, token); node = codeflash_output # 6.36μs -> 4.85μs (31.0% faster)
# codeflash_output is used to check that the output of the original code is the same as that of the optimized code.

To edit these changes git checkout codeflash/optimize-do_for-mhcvgfvr and push.