Output Formatting Options

Python provides multiple ways to format output for display or writing to files. The simplest methods are expression statements and the print() function, but for more sophisticated formatting, you have several options:

Formatted String Literals (f-strings)

Introduced in Python 3.6, f-strings provide a concise way to embed expressions inside string literals:

year = 2016
event = 'Referendum'
print(f'Results of the {year} {event}')
# Output: Results of the 2016 Referendum

F-strings support formatting specifications after expressions:

import math
print(f'Pi value: {math.pi:.3f}')  # Rounds to 3 decimal places

For aligning columns:

table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 7678}
for name, phone in table.items():
    print(f'{name:10} ==> {phone:10d}')

The str.format() Method

This method provides more explicit control over formatting:

print('We are the {} who say "{}!"'.format('knights', 'Ni'))

You can reference values by position or keyword:

print('{0} and {1}'.format('spam', 'eggs'))
print('This {food} is {adj}.'.format(food='spam', adj='horrible'))

Manual String Formatting

For complete control, you can use string methods:

for x in range(1, 11):
    print(str(x).rjust(2), str(x*x).rjust(3), str(x*x*x).rjust(4))

String methods include:

• str.rjust(width) – Right justify
• str.ljust(width) – Left justify
• str.center(width) – Center
• str.zfill(width) – Pad with zeros

String Representation

For debugging, use repr() and str() to convert values to strings:

s = 'Hello, world.'
print(str(s))   # Human-readable
print(repr(s))  # Interpreter-readable

Working with Files

Opening Files

Use the open() function with recommended encoding:

with open('workfile', 'r', encoding='utf-8') as f:
    contents = f.read()

File modes include:

• 'r' – Read (default)
• 'w' – Write (overwrites)
• 'a' – Append
• 'r+' – Read and write
• 'b' – Binary mode

File Object Methods

Key methods for reading:

• f.read(size) – Reads specified amount
• f.readline() – Reads single line
• f.readlines() – Returns list of lines
• Iteration – Memory efficient line reading

Writing methods:

• f.write(string) – Writes string to file
• f.tell() – Returns current position
• f.seek(offset) – Changes file position

JSON Data Handling

For structured data, use the json module:

import json

# Serialize
data = {'name': 'John', 'age': 30}
with open('data.json', 'w') as f:
    json.dump(data, f)

# Deserialize
with open('data.json', 'r') as f:
    loaded = json.load(f)

Note: JSON files must use UTF-8 encoding.

Best Practices

1. Always use with statements for file handling to ensure proper closing
2. Specify encoding (preferably UTF-8) when opening text files
3. Use binary mode ('b') for non-text files
4. Prefer f-strings for most string formatting needs
5. Use JSON for structured data storage
6. Consider repr() for debugging output to see exact values

Remember that file paths are system-dependent – use raw strings (r'path') or forward slashes for Windows paths to avoid escape character issues.