tools-only Gantt Chart Generator
Business Case
Problem Statement
Schedule visualization challenges:
- Complex task dependencies
- Progress tracking
- Critical path visibility
- Multi-level WBS display
Solution
Generate interactive Gantt charts from schedule data with dependency visualization, progress tracking, and export capabilities.
Technical Implementation
import pandas as pd
from typing import Dict, Any, List, Optional
from dataclasses import dataclass, field
from datetime import date, timedelta
from enum import Enum
class TaskStatus(Enum):
NOT_STARTED = "not_started"
IN_PROGRESS = "in_progress"
COMPLETED = "completed"
DELAYED = "delayed"
class DependencyType(Enum):
FS = "finish_to_start"
SS = "start_to_start"
FF = "finish_to_finish"
SF = "start_to_finish"
@dataclass
class Task:
task_id: str
name: str
start_date: date
end_date: date
wbs_code: str = ""
progress: float = 0 # 0-100
status: TaskStatus = TaskStatus.NOT_STARTED
assignee: str = ""
level: int = 0
is_milestone: bool = False
is_summary: bool = False
parent_id: str = ""
@dataclass
class Dependency:
predecessor_id: str
successor_id: str
dep_type: DependencyType = DependencyType.FS
lag: int = 0
class GanttChartGenerator:
"""Generate Gantt charts for construction scheduling."""
def __init__(self, project_name: str):
self.project_name = project_name
self.tasks: Dict[str, Task] = {}
self.dependencies: List[Dependency] = []
def add_task(self, task: Task):
"""Add task to chart."""
self.tasks[task.task_id] = task
def add_dependency(self, predecessor_id: str, successor_id: str,
dep_type: DependencyType = DependencyType.FS,
lag: int = 0):
"""Add dependency between tasks."""
self.dependencies.append(Dependency(
predecessor_id=predecessor_id,
successor_id=successor_id,
dep_type=dep_type,
lag=lag
))
def import_from_df(self, df: pd.DataFrame):
"""Import tasks from DataFrame."""
for _, row in df.iterrows():
task = Task(
task_id=str(row['task_id']),
name=row['name'],
start_date=pd.to_datetime(row['start_date']).date(),
end_date=pd.to_datetime(row['end_date']).date(),
wbs_code=str(row.get('wbs_code', '')),
progress=float(row.get('progress', 0)),
level=int(row.get('level', 0)),
is_milestone=bool(row.get('is_milestone', False)),
is_summary=bool(row.get('is_summary', False)),
parent_id=str(row.get('parent_id', ''))
)
self.add_task(task)
def get_project_range(self) -> tuple:
"""Get project date range."""
if not self.tasks:
return (date.today(), date.today())
min_date = min(t.start_date for t in self.tasks.values())
max_date = max(t.end_date for t in self.tasks.values())
return (min_date, max_date)
def get_duration(self, task_id: str) -> int:
"""Get task duration in days."""
task = self.tasks.get(task_id)
if task:
return (task.end_date - task.start_date).days + 1
return 0
def generate_text_gantt(self, width: int = 60) -> str:
"""Generate text-based Gantt chart."""
if not self.tasks:
return "No tasks"
lines = []
start, end = self.get_project_range()
total_days = (end - start).days + 1
scale = width / total_days if total_days > 0 else 1
# Header
lines.append(f"Project: {self.project_name}")
lines.append(f"Period: {start} to {end}")
lines.append("-" * (40 + width))
# Tasks
for task in sorted(self.tasks.values(), key=lambda t: (t.level, t.start_date)):
indent = " " * task.level
name = f"{indent}{task.name}"[:35].ljust(35)
# Bar position
bar_start = int((task.start_date - start).days * scale)
bar_length = max(1, int(self.get_duration(task.task_id) * scale))
# Progress bar
progress_length = int(bar_length * task.progress / 100)
bar = " " * bar_start
bar += "█" * progress_length
bar += "░" * (bar_length - progress_length)
bar = bar[:width].ljust(width)
status_char = "◆" if task.is_milestone else "│"
lines.append(f"{name} {status_char}{bar}│ {task.progress:.0f}%")
return "\n".join(lines)
def generate_mermaid_gantt(self) -> str:
"""Generate Mermaid Gantt diagram."""
lines = [
"gantt",
f" title {self.project_name}",
" dateFormat YYYY-MM-DD",
""
]
# Group by WBS prefix
sections = {}
for task in self.tasks.values():
section = task.wbs_code.split('.')[0] if task.wbs_code else "Tasks"
if section not in sections:
sections[section] = []
sections[section].append(task)
for section, tasks in sections.items():
lines.append(f" section {section}")
for task in sorted(tasks, key=lambda t: t.start_date):
duration = self.get_duration(task.task_id)
status = ""
if task.status == TaskStatus.COMPLETED:
status = "done, "
elif task.status == TaskStatus.IN_PROGRESS:
status = "active, "
if task.is_milestone:
lines.append(f" {task.name} :milestone, {task.start_date}, 0d")
else:
lines.append(f" {task.name} :{status}{task.task_id}, {task.start_date}, {duration}d")
return "\n".join(lines)
def generate_html_gantt(self) -> str:
"""Generate HTML/CSS Gantt chart."""
start, end = self.get_project_range()
total_days = (end - start).days + 1
html = f"""
<!DOCTYPE html>
<html>
<head>
<title>Gantt Chart - {self.project_name}</title>
<style>
.gantt {{ font-family: Arial, sans-serif; }}
.task {{ display: flex; margin: 2px 0; height: 25px; align-items: center; }}
.task-name {{ width: 200px; padding-right: 10px; font-size: 12px; }}
.task-bar {{ position: relative; height: 20px; background: #e0e0e0; flex: 1; }}
.bar {{ position: absolute; height: 100%; }}
.bar-fill {{ background: #4CAF50; }}
.bar-progress {{ background: #2196F3; }}
.milestone {{ width: 10px; height: 10px; background: #FF5722; transform: rotate(45deg); margin-left: 10px; }}
</style>
</head>
<body>
<div class="gantt">
<h2>{self.project_name}</h2>
<p>{start} - {end}</p>
"""
for task in sorted(self.tasks.values(), key=lambda t: (t.level, t.start_date)):
left = ((task.start_date - start).days / total_days) * 100
width = (self.get_duration(task.task_id) / total_days) * 100
progress_width = width * task.progress / 100
indent = " " * (task.level * 4)
if task.is_milestone:
html += f'<div class="task"><div class="task-name">{indent}{task.name}</div><div class="task-bar"><div class="milestone" style="left:{left}%"></div></div></div>\n'
else:
html += f'''<div class="task">
<div class="task-name">{indent}{task.name}</div>
<div class="task-bar">
<div class="bar bar-fill" style="left:{left}%; width:{width}%"></div>
<div class="bar bar-progress" style="left:{left}%; width:{progress_width}%"></div>
</div>
</div>\n'''
html += "</div></body></html>"
return html
def get_critical_path(self) -> List[str]:
"""Identify critical path tasks (simplified)."""
if not self.dependencies:
return [t.task_id for t in sorted(self.tasks.values(), key=lambda x: x.end_date)[-5:]]
# Find tasks with no slack (simplified approach)
critical = []
_, project_end = self.get_project_range()
for task in self.tasks.values():
if task.end_date == project_end:
critical.append(task.task_id)
# Trace predecessors
for dep in self.dependencies:
if dep.successor_id == task.task_id:
critical.append(dep.predecessor_id)
return list(set(critical))
def export_to_excel(self, output_path: str) -> str:
"""Export Gantt data to Excel."""
with pd.ExcelWriter(output_path, engine='openpyxl') as writer:
# Tasks
tasks_df = pd.DataFrame([{
'ID': t.task_id,
'WBS': t.wbs_code,
'Name': t.name,
'Start': t.start_date,
'End': t.end_date,
'Duration': self.get_duration(t.task_id),
'Progress': t.progress,
'Status': t.status.value,
'Level': t.level
} for t in self.tasks.values()])
tasks_df.to_excel(writer, sheet_name='Tasks', index=False)
# Dependencies
deps_df = pd.DataFrame([{
'Predecessor': d.predecessor_id,
'Successor': d.successor_id,
'Type': d.dep_type.value,
'Lag': d.lag
} for d in self.dependencies])
deps_df.to_excel(writer, sheet_name='Dependencies', index=False)
return output_path
Quick Start
from datetime import date, timedelta
# Create Gantt chart
gantt = GanttChartGenerator("Office Building A")
# Add tasks
gantt.add_task(Task("T1", "Foundation", date(2024, 6, 1), date(2024, 6, 30), "01", progress=100))
gantt.add_task(Task("T2", "Structure", date(2024, 7, 1), date(2024, 9, 30), "02", progress=60))
gantt.add_task(Task("T3", "MEP Rough-in", date(2024, 8, 1), date(2024, 10, 31), "03", progress=30))
gantt.add_task(Task("M1", "Topping Out", date(2024, 9, 30), date(2024, 9, 30), is_milestone=True))
# Add dependencies
gantt.add_dependency("T1", "T2")
gantt.add_dependency("T2", "T3")
# Generate text Gantt
print(gantt.generate_text_gantt())
Common Use Cases
1. Mermaid Diagram
mermaid = gantt.generate_mermaid_gantt()
print(mermaid) # Copy to Mermaid editor
2. HTML Export
html = gantt.generate_html_gantt()
with open("gantt.html", "w") as f:
f.write(html)
3. Critical Path
critical = gantt.get_critical_path()
print(f"Critical tasks: {critical}")
Resources
- DDC Book: Chapter 3.3 - 4D Scheduling and BIM
- Website: https://datadrivenconstruction.io