File Handling and Context Managers¶

File handling in Python involves opening, reading, writing, and closing files on the local filesystem.

The `with` Statement (Context Manager)¶

It is good practice to use the with keyword when dealing with file objects. The advantage is that the file is properly closed after its suite finishes, even if an exception is raised at any point:

Syntax¶

with open(filename, mode, encoding="utf-8") as file_handle:
    # file operations

Example: Writing and Reading a Text File

# 1. Writing to a file
with open("notes.txt", "w", encoding="utf-8") as f:
    f.write("Line 1: Python documentation\n")
    f.write("Line 2: Production ready\n")

# 2. Reading the file back
with open("notes.txt", "r", encoding="utf-8") as f:
    content = f.read()

print(content)

Output

Line 1: Python documentation Line 2: Production ready

File Access Modes¶

Mode	Meaning	Creates File if Missing?	Truncates (Overwrites)?
`'r'`	Read only (default)	No (raises `FileNotFoundError`)	No
`'w'`	Write only	Yes	Yes
`'a'`	Append (writes to end)	Yes	No
`'r+'`	Read and Write	No	No
`'b'`	Binary mode (e.g. `'rb'`, `'wb'`)	-	-

Reading Files Line by Line¶

For large files, iterating directly over the file object avoids loading the entire file into RAM:

with open("large_log.txt", "r", encoding="utf-8") as file:
    for line_number, line in enumerate(file, start=1):
        if "ERROR" in line:
            print(f"Line {line_number}: {line.strip()}")

Modern Path Handling with `pathlib`¶

The pathlib module offers classes representing filesystem paths with semantics appropriate for different operating systems:

Example: Using pathlib.Path

from pathlib import Path

# Create path object using / operator
data_dir = Path("data") / "reports"
file_path = data_dir / "summary.txt"

# Create directories if they do not exist
data_dir.mkdir(parents=True, exist_ok=True)

# Write and read text directly
file_path.write_text("All tests passing.", encoding="utf-8")
print("File Content:", file_path.read_text(encoding="utf-8"))
print("File Exists:", file_path.exists())