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"""Utilities for truncating assertion output.
Current default behaviour is to truncate assertion explanations at
~8 terminal lines, unless running in "-vv" mode or running on CI.
"""
from typing import List
from typing import Optional
from _pytest.assertion import util
from _pytest.nodes import Item
DEFAULT_MAX_LINES = 8
DEFAULT_MAX_CHARS = 8 * 80
USAGE_MSG = "use '-vv' to show"
def truncate_if_required(
explanation: List[str], item: Item, max_length: Optional[int] = None
) -> List[str]:
"""Truncate this assertion explanation if the given test item is eligible."""
if _should_truncate_item(item):
return _truncate_explanation(explanation)
return explanation
def _should_truncate_item(item: Item) -> bool:
"""Whether or not this test item is eligible for truncation."""
verbose = item.config.option.verbose
return verbose < 2 and not util.running_on_ci()
def _truncate_explanation(
input_lines: List[str],
max_lines: Optional[int] = None,
max_chars: Optional[int] = None,
) -> List[str]:
"""Truncate given list of strings that makes up the assertion explanation.
Truncates to either 8 lines, or 640 characters - whichever the input reaches
first, taking the truncation explanation into account. The remaining lines
will be replaced by a usage message.
"""
if max_lines is None:
max_lines = DEFAULT_MAX_LINES
if max_chars is None:
max_chars = DEFAULT_MAX_CHARS
# Check if truncation required
input_char_count = len("".join(input_lines))
# The length of the truncation explanation depends on the number of lines
# removed but is at least 68 characters:
# The real value is
# 64 (for the base message:
# '...\n...Full output truncated (1 line hidden), use '-vv' to show")'
# )
# + 1 (for plural)
# + int(math.log10(len(input_lines) - max_lines)) (number of hidden line, at least 1)
# + 3 for the '...' added to the truncated line
# But if there's more than 100 lines it's very likely that we're going to
# truncate, so we don't need the exact value using log10.
tolerable_max_chars = (
max_chars + 70 # 64 + 1 (for plural) + 2 (for '99') + 3 for '...'
)
# The truncation explanation add two lines to the output
tolerable_max_lines = max_lines + 2
if (
len(input_lines) <= tolerable_max_lines
and input_char_count <= tolerable_max_chars
):
return input_lines
# Truncate first to max_lines, and then truncate to max_chars if necessary
truncated_explanation = input_lines[:max_lines]
truncated_char = True
# We reevaluate the need to truncate chars following removal of some lines
if len("".join(truncated_explanation)) > tolerable_max_chars:
truncated_explanation = _truncate_by_char_count(
truncated_explanation, max_chars
)
else:
truncated_char = False
truncated_line_count = len(input_lines) - len(truncated_explanation)
if truncated_explanation[-1]:
# Add ellipsis and take into account part-truncated final line
truncated_explanation[-1] = truncated_explanation[-1] + "..."
if truncated_char:
# It's possible that we did not remove any char from this line
truncated_line_count += 1
else:
# Add proper ellipsis when we were able to fit a full line exactly
truncated_explanation[-1] = "..."
return truncated_explanation + [
"",
f"...Full output truncated ({truncated_line_count} line"
f"{'' if truncated_line_count == 1 else 's'} hidden), {USAGE_MSG}",
]
def _truncate_by_char_count(input_lines: List[str], max_chars: int) -> List[str]:
# Find point at which input length exceeds total allowed length
iterated_char_count = 0
for iterated_index, input_line in enumerate(input_lines):
if iterated_char_count + len(input_line) > max_chars:
break
iterated_char_count += len(input_line)
# Create truncated explanation with modified final line
truncated_result = input_lines[:iterated_index]
final_line = input_lines[iterated_index]
if final_line:
final_line_truncate_point = max_chars - iterated_char_count
final_line = final_line[:final_line_truncate_point]
truncated_result.append(final_line)
return truncated_result
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