Built-in Types

Reference for Python built-in types supported by Shed Skin

Shed Skin supports the core Python built-in types with static type semantics. This page documents the available operations and methods for each type.

Numeric Types

int

Integer type. By default, integers are 32-bit signed integers on most architectures.

Size Configuration:

• Default: 32-bit signed integer (on most architectures)
• Use --int64 flag for 64-bit integers
• Use --int32 flag to explicitly specify 32-bit
• Use --int128 flag for 128-bit integers

Supported Operations:

a = 42
b = 10

# Arithmetic
c = a + b      # Addition
c = a - b      # Subtraction
c = a * b      # Multiplication
c = a / b      # True division (returns float)
c = a // b     # Floor division
c = a % b      # Modulo
c = a ** b     # Exponentiation
c = divmod(a, b)  # Returns (quotient, remainder)

# Bitwise operations
c = a & b      # AND
c = a | b      # OR
c = a ^ b      # XOR
c = a << b     # Left shift
c = a >> b     # Right shift
c = ~a         # Invert

# Unary operations
c = -a         # Negation
c = +a         # Unary plus
c = abs(a)     # Absolute value

# Comparison
if a == b: pass
if a != b: pass
if a < b: pass
if a <= b: pass
if a > b: pass
if a >= b: pass

Supported Methods:

n = 42

# Count set bits
count = n.bit_count()      # Number of 1 bits in binary

# Bit length
length = n.bit_length()     # Number of bits needed to represent n

# Type check
if n.is_integer():          # Always True for int
    pass

Important Notes:

• No arbitrary-precision arithmetic (unlike CPython)
• Integer overflow behavior follows C++ semantics
• Use appropriate size flag for your data range needs

float

Floating-point number type.

Size Configuration:

• Default: 64-bit double precision
• Use --float32 flag for 32-bit single precision
• Use --float64 flag to explicitly specify 64-bit

Supported Operations:

a = 3.14
b = 2.0

# Arithmetic (same as int)
c = a + b
c = a - b
c = a * b
c = a / b
c = a // b
c = a % b
c = a ** b

# Unary operations
c = -a
c = +a
c = abs(a)

# Comparison
if a == b: pass
if a < b: pass
# ... etc

Supported Methods:

x = 3.5

# Type check
if x.is_integer():          # Check if value is integral
    pass

Mixing int and float:

a = 5        # int
b = 2.0      # float
c = a + b    # Result is float (7.0)
d = a / 2    # Result is float (2.5)

bool

Boolean type with values True and False.

Supported Operations:

a = True
b = False

# Logical operations
c = a and b
c = a or b
c = not a

# Bitwise operations (bool behaves like int)
c = a & b
c = a | b
c = a ^ b

# Comparison
if a == b: pass
if a != b: pass

# Arithmetic (bool acts as int: True=1, False=0)
c = a + b      # Valid: True + False = 1

complex

Complex number type.

Supported Operations:

z1 = 3 + 4j
z2 = 1 + 2j

# Arithmetic
z3 = z1 + z2
z3 = z1 - z2
z3 = z1 * z2
z3 = z1 / z2

# Unary
z3 = -z1
z3 = +z1

# Access components
real_part = z1.real
imag_part = z1.imag

# Absolute value (magnitude)
mag = abs(z1)

Sequence Types

str

String type for text data.

Character Encoding:

• Currently restricted to 1-byte characters
• No full Unicode/UTF-8 support
• ASCII and Latin-1 work fine

Supported Operations:

s = "hello"
t = "world"

# Concatenation
u = s + " " + t        # "hello world"

# Repetition
u = s * 3               # "hellohellohello"

# Indexing
ch = s[0]               # 'h'
ch = s[-1]              # 'o'

# Slicing
sub = s[1:4]            # "ell"
sub = s[::2]            # "hlo"
sub = s[::-1]           # "olleh" (reverse)

# Length
n = len(s)              # 5

# Membership
if "ell" in s:          # True
    pass

# Comparison
if s == t: pass
if s < t: pass          # Lexicographic comparison

# Iteration
for ch in s:
    print(ch)

Supported Methods:

s = "Hello World"

# Case conversion
s.upper()               # "HELLO WORLD"
s.lower()               # "hello world"
s.capitalize()          # "Hello world"
s.title()               # "Hello World"
s.swapcase()            # "hELLO wORLD"

# Search
s.find("World")         # 6 (or -1 if not found)
s.index("World")        # 6 (raises exception if not found)
s.count("l")            # 3
s.startswith("Hello")   # True
s.endswith("World")     # True

# Split and join
words = s.split()       # ["Hello", "World"]
parts = s.split("l")    # ["He", "", "o Wor", "d"]
s2 = "-".join(words)    # "Hello-World"

# Strip whitespace
s = "  hello  "
s.strip()               # "hello"
s.lstrip()              # "hello  "
s.rstrip()              # "  hello"

# Replace
s.replace("World", "Python")  # "Hello Python"

# Type checks
"123".isdigit()         # True
"abc".isalpha()         # True
"abc123".isalnum()      # True
"   ".isspace()         # True

# Formatting
"{} {}".format("Hello", "World")  # "Hello World"
"%s %d" % ("count", 42)            # "count 42"

bytes

Immutable sequence of bytes.

Supported Operations:

b = b"hello"

# Similar to str operations
len(b)                  # 5
b[0]                    # 104 (ASCII value of 'h')
b[1:4]                  # b"ell"
b + b" world"           # b"hello world"

# Conversion
b.decode()              # Convert to str (default ASCII)
s = "hello"
s.encode()              # Convert str to bytes

bytearray

Mutable sequence of bytes.

Supported Operations:

ba = bytearray(b"hello")

# All bytes operations plus:
ba[0] = 72              # Modify in place -> b"Hello"
ba.append(33)           # Append byte
ba.extend(b"!!")        # Extend with bytes

list

Mutable sequence type.

Type Restriction: All elements must be of the same type (or compatible types with common base).

Supported Operations:

lst = [1, 2, 3, 4, 5]

# Indexing
x = lst[0]              # 1
x = lst[-1]             # 5

# Slicing
sub = lst[1:4]          # [2, 3, 4]
sub = lst[::2]          # [1, 3, 5]

# Length
n = len(lst)            # 5

# Membership
if 3 in lst:            # True
    pass

# Concatenation
lst2 = [6, 7]
lst3 = lst + lst2       # [1, 2, 3, 4, 5, 6, 7]

# Repetition
lst3 = [0] * 5          # [0, 0, 0, 0, 0]

# Iteration
for x in lst:
    print(x)

# Comprehensions
squares = [x*x for x in lst]              # [1, 4, 9, 16, 25]
evens = [x for x in lst if x % 2 == 0]    # [2, 4]

Supported Methods:

lst = [3, 1, 4, 1, 5]

# Modify
lst.append(9)           # [3, 1, 4, 1, 5, 9]
lst.insert(0, 2)        # [2, 3, 1, 4, 1, 5, 9]
lst.extend([2, 6])      # Add multiple elements
lst[1] = 10             # Modify element

# Remove
lst.remove(1)           # Remove first occurrence
x = lst.pop()           # Remove and return last
x = lst.pop(0)          # Remove and return at index
lst.clear()             # Remove all elements

# Reorder
lst.sort()              # Sort in place
lst.reverse()           # Reverse in place

# Search
idx = lst.index(4)      # Find index of element
count = lst.count(1)    # Count occurrences

# Copy
lst2 = lst.copy()       # Shallow copy

tuple

Immutable sequence type.

Type Restriction:

• All elements same type for tuples of any length
• Mixed types allowed for length-2 tuples only

Supported Operations:

t = (1, 2, 3)

# Same readonly operations as list
x = t[0]
sub = t[1:]
n = len(t)
if 2 in t: pass

# Cannot modify
# t[0] = 5  # ERROR

# Packing/unpacking
a, b, c = t

# Mixed-type tuples (length 2 only)
pair = (42, "hello")    # OK
triple = (1, "a", 2.0)  # NOT SUPPORTED

Supported Methods:

t = (1, 2, 3, 2, 1)

t.count(2)              # 2
t.index(3)              # 2

Mapping Type

dict

Dictionary mapping type.

Type Restriction: Keys must be of one type, values must be of one type. Keys must be hashable.

Supported Operations:

d = {'a': 1, 'b': 2, 'c': 3}

# Access
x = d['a']              # 1
x = d.get('d', 0)       # 0 (default)

# Modify
d['d'] = 4              # Add/update
del d['a']              # Remove

# Membership (checks keys)
if 'b' in d:            # True
    pass

# Length
n = len(d)              # Number of key-value pairs

# Iteration
for key in d:
    print(key, d[key])

for key, value in d.items():
    print(key, value)

Supported Methods:

d = {'a': 1, 'b': 2}

# Keys, values, items
keys = d.keys()         # View of keys
values = d.values()     # View of values
items = d.items()       # View of (key, value) pairs

# Get/set
x = d.get('c', 0)       # Get with default
x = d.setdefault('c', 3)  # Get or set default

# Remove
x = d.pop('a')          # Remove and return
key, val = d.popitem()  # Remove and return arbitrary pair

# Update
d.update({'c': 3, 'd': 4})

# Copy/clear
d2 = d.copy()           # Shallow copy
d.clear()               # Remove all items

# Create from keys
d = dict.fromkeys(['a', 'b'], 0)  # {'a': 0, 'b': 0}

Set Types

set

Unordered collection of unique elements.

Type Restriction: All elements must be of the same type and hashable.

Supported Operations:

s = {1, 2, 3, 4, 5}
t = {4, 5, 6, 7, 8}

# Set operations
u = s | t               # Union: {1,2,3,4,5,6,7,8}
u = s & t               # Intersection: {4,5}
u = s - t               # Difference: {1,2,3}
u = s ^ t               # Symmetric difference: {1,2,3,6,7,8}

# Membership
if 3 in s:              # True
    pass

# Length
n = len(s)              # 5

# Comparison
if s <= t:              # Subset
    pass
if s < t:               # Proper subset
    pass

Supported Methods:

s = {1, 2, 3}

# Add/remove
s.add(4)                # Add element
s.remove(2)             # Remove (raises KeyError if not found)
s.discard(5)            # Remove if present
x = s.pop()             # Remove and return arbitrary element
s.clear()               # Remove all

# Set operations (method form)
s = {1, 2, 3}
t = {3, 4, 5}
s.union(t)              # {1,2,3,4,5}
s.intersection(t)       # {3}
s.difference(t)         # {1,2}
s.symmetric_difference(t)  # {1,2,4,5}

# In-place operations
s.update(t)             # s |= t
s.intersection_update(t)  # s &= t
s.difference_update(t)  # s -= t

# Comparison
s.issubset(t)
s.issuperset(t)
s.isdisjoint(t)

# Copy
s2 = s.copy()

frozenset

Immutable set type. Supports same operations as set except modifications.

fs = frozenset([1, 2, 3])

# Read-only operations only
if 2 in fs: pass
n = len(fs)
u = fs | {4, 5}
# fs.add(4)  # ERROR - immutable

Type Checking and Conversion

# Built-in type constructors
x = int("42")           # String to int
x = float("3.14")       # String to float
s = str(42)             # Int to string
b = bool(x)             # Convert to bool

# Collection constructors
lst = list((1,2,3))     # Tuple to list
t = tuple([1,2,3])      # List to tuple
s = set([1,2,2,3])      # List to set (removes duplicates)
d = dict([('a',1), ('b',2)])  # List of pairs to dict

None Type

None represents absence of a value.

Important Restriction: None can only be mixed with non-scalar types (not with int, float, bool, or complex).

# OK - list can be None
lst = [1, 2, 3]
lst = None              # Valid

# OK - object can be None
obj = MyClass()
obj = None              # Valid

# NOT OK - scalar cannot be None
x = 42
# x = None              # ERROR

# Instead use special sentinel value
x = -1                  # Use -1 to indicate "no value"

Performance Notes

• List operations: Appending is O(1) amortized. Prefer append() over + in loops.
• String concatenation: Use "".join(list) for concatenating many strings instead of + in a loop.
• Dictionary/set operations: Hash-based, typically O(1) for lookup/insert.
• Integer size: Smaller integer sizes can improve performance and memory usage if your values fit.
• Float size: 32-bit floats use less memory but have less precision.

See Also

• Supported Modules - Standard library module reference
• Limitations - Type system limitations and restrictions