Strings, numbers, and formatting

Strings, numbers, and the formatting between them are the bread and butter of any analysis pipeline. Get fluent at f-strings, integer-vs-float arithmetic, and basic string methods, and you can move data around with confidence.

Strings — the basics

Strings can use single or double quotes interchangeably. Triple quotes (''' or """) allow multi-line strings. Strings are immutable: methods return new strings rather than modifying in place.

name = 'Kenya'
name.upper()           # 'KENYA' — returns a new string
name.lower()           # 'kenya'
name.replace('K', 'B') # 'Benya'
len(name)              # 5
'Africa' in 'sub-Saharan Africa'  # True

f-strings — the formatting tool you'll use most

Python 3.6+ introduced f-strings, which allow you to embed expressions inside string literals using curly braces. They are by far the cleanest formatting tool in the language.

rate = 0.1235
print(f'The CBR is {rate:.2%}')      # 'The CBR is 12.35%'
print(f'KES {1234567:,.0f}')          # 'KES 1,234,567'

name, gdp = 'Kenya', 110_000
print(f'{name}: ${gdp:,}M')           # 'Kenya: $110,000M'

Integer vs float division

In Python 3, the / operator always returns a float, even for integer operands. Use // for integer (floor) division when you want an int result.

10 / 3      # 3.3333333333333335 (float)
10 // 3     # 3 (int)
10 % 3      # 1 (modulo)
10 ** 3     # 1000 (exponentiation)

Numbers — three things to know

• Integer overflow doesn't exist in Python — ints grow as needed.
• Floats are IEEE 754, with the usual precision warnings: 0.1 + 0.2 == 0.3 is False because 0.1 has no exact binary representation.
• Use the decimal module for money or any context where 0.1 + 0.2 == 0.3 must be True.