Control flow structures¶

Control flow in Algorand Python is similar to standard Python control flow, with support for if statements, while loops, for loops, and match statements.

If statements¶

If statements work the same as Python. The conditions must be an expression that evaluates to bool, which can include a String or Uint64 among others.

if condition:
    # block of code to execute if condition is True
elif condition2:
    # block of code to execute if condition is False and condition2 is True
else:
    # block of code to execute if condition and condition2 are both False

See full example.

Ternary conditions¶

Ternary conditions work the same as Python. The condition must be an expression that evaluates to bool, which can include a String or Uint64 among others.

value1 = UInt64(5)
value2 = String(">6") if value1 > 6 else String("<=6")

While loops¶

While loops work the same as Python. The condition must be an expression that evaluates to bool, which can include a String or Uint64 among others.

You can use break and continue.

while condition:
    # block of code to execute if condition is True

Note: we don’t currently have support for while-else statements.

See full example.

For Loops¶

For loops are used to iterate over sequences, ranges and ARC-4 arrays. They work the same as Python.

Algorand Python provides functions like uenumerate and urange to facilitate creating sequences and ranges; in-built Python reversed method works with these.

uenumerate is similar to Python’s built-in enumerate function, but for UInt64 numbers; it allows you to loop over a sequence and have an automatic counter.
urange is a function that generates a sequence of Uint64 numbers, which you can iterate over.
reversed returns a reversed iterator of a sequence.

Here is an example of how you can use these functions in a contract:

test_array = arc4.StaticArray(arc4.UInt8(), arc4.UInt8(), arc4.UInt8(), arc4.UInt8())

# urange: reversed items, forward index

for index, item in uenumerate(reversed(urange(4))):
    test_array[index] = arc4.UInt8(item)

assert test_array.bytes == Bytes.from_hex("03020100")

Note: we don’t currently have support for for-else statements.

See full examples.

Match Statements¶

Match statements work the same as Python and work for […]

match value:
    case pattern1:
        # block of code to execute if pattern1 matches
    case pattern2:
        # block of code to execute if pattern2 matches
    case _:
        # Fallback

Note: Captures and patterns are not supported. Currently, there is only support for basic case/switch functionality; pattern matching and guard clauses are not currently supported.

See full example.