Swap

class defipy.process.Swap()

Swap exact token_in for token_out on an initialized pool. The output amount is determined by the pool’s invariant — constant product for V2, concentrated-liquidity ticks for V3, weighted geometric mean for Balancer, the amplification-adjusted curve for Stableswap.

Cross-protocol: dispatches to the underlying protocol implementation. Available on Uniswap V2, Uniswap V3, Balancer, and Stableswap.

Methods

apply

out = Swap().apply(pool, token_in, user, amount_in)

Execute the swap. Pool reserves update; the user’s balance of token_out increases by the returned amount.

Parameters

Name	Type	Description
`pool`	exchange	Pool instance to swap on.
`token_in`	`ERC20`	The token being swapped in. The other side of the pair is the token being swapped out.
`user`	`str`	User address (string identifier) executing the swap.
`amount_in`	`float`	Amount of `token_in` to swap.

Returns

Name	Type	Description
`out`	`float`	Amount of `token_out` the user receives, net of pool fees.

Example

Swap token1 for token0

from defipy import *

user_nm = 'user'
eth_amount = 1000
tkn_amount = 100000

tkn = ERC20("TKN", "0x111")
eth = ERC20("ETH", "0x09")
exchg_data = UniswapExchangeData(tkn0 = eth, tkn1 = tkn, symbol="LP", address="0x011")

factory = UniswapFactory("ETH pool factory", "0x2")
lp = factory.deploy(exchg_data)

Join().apply(lp, user_nm, eth_amount, tkn_amount)
lp.summary()

out = Swap().apply(lp, tkn, user_nm, 1000)
lp.summary()

Exchange ETH-TKN (LP) Reserves: ETH = 1000.0, TKN = 100000.0 Liquidity: 10000.0 Exchange ETH-TKN (LP) Reserves: ETH = 990.1284196560293, TKN = 101000.0 Liquidity: 10000.0

Swap token0 for token1

out = Swap().apply(lp, eth, user_nm, 10)
lp.summary()

Exchange ETH-TKN (LP) Reserves: ETH = 1010.0, TKN = 99012.84196560294 Liquidity: 10000.0

Notes

Fee handling is protocol-specific. V2 hard-codes 30 bps inside get_amount_out. V3 reads the fee tier from pool.fee (in pips: 100 = 0.01%, 500 = 0.05%, 3000 = 0.3%, 10000 = 1%). Balancer’s SWAP_FEE is 0.25%. Stableswap fees are configured per-pool.
Slippage is not capped by Swap itself. If you need slippage protection, compute the expected output via LPQuote first and verify the realized output against your tolerance after the call.
Swap is symmetric. Reversing token_in reverses the direction; pool state behaves consistently.
Trading LP tokens. Some primitives accept an LP-token instance for token_in when the pool is layered (an LP token of one pool acting as a token in another). The example tutorial covers this case.