Python Developer Fundamentals

Built-in types

• int, float, bool, str, NoneType
• Collections: list (mutable), tuple (immutable), dict, set
• Check a type with type(x); compare types with isinstance(x, int).

Operators that trip people up

• / always returns a float: 10 / 2 gives 5.0.
• // is floor division (rounds towards minus infinity): 7 // 2 is 3 but -7 // 2 is -4.
• % gives the remainder with the sign of the divisor: 7 % 2 is 1.
• is power: 2 10 is 1024.

Truthiness

Empty values are False: 0, 0.0, "", [], {}, set(), None. Everything else is True – including the string "0".

print(bool(""), bool("0"), bool([]))   # False True False

Strings

Strings are immutable sequences. Slicing is s[start:stop:step], stop excluded.

s = "placement"
print(s[2:6])    # acem
print(s[::-1])   # tnemecalp  (reversed)
print(s.upper(), s.count("e"), len(s))   # PLACEMENT 2 9
name = "Anu"
print(f"Hello, {name}!")   # f-strings for formatting

Mutability matters

Assigning a list to a new name does not copy it – both names point to the same object. Use list.copy() or slicing a[:] to copy.

a = [1, 2, 3]
b = a
b.append(4)
print(a)   # [1, 2, 3, 4]