WithdrawSwap

class defipy.process.WithdrawSwap()

Single-sided withdrawal, also called a zap-out. The caller wants to leave the pool holding only one token from the pair. The primitive performs an approximate 50/50 withdrawal, swaps the unwanted side back into the desired token, and returns the user’s full position in the desired token.

Available on Uniswap V2 and Uniswap V3 only. Balancer and Stableswap support is tracked for a later release.

Methods

apply

amount_out = WithdrawSwap().apply(pool, token_out, user, amount_out_target)

Withdraw the user’s stake from pool, returning approximately amount_out_target of token_out. The primitive burns LP tokens, removes both sides, swaps the non-target side, and returns the target side.

Parameters

Name	Type	Description
`pool`	exchange	Pool instance to withdraw from. V2 or V3 only.
`token_out`	`ERC20`	The token the user wants to leave with.
`user`	`str`	User address (string identifier) whose LP tokens are burned.
`amount_out_target`	`float`	Target amount of `token_out` to receive.

Returns

Name	Type	Description
`amount_out`	`float`	The actual amount of `token_out` returned to the user (slightly less than the target due to swap fees on the rebalancing leg).

Example

Withdraw exact 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)
expected_amount_out = WithdrawSwap().apply(lp, eth, user_nm, 1)
lp.summary()

Exchange ETH-TKN (LP) Reserves: ETH = 999.0, TKN = 100000.0 Liquidity: 9994.991239989282

Withdraw exact token1

expected_amount_out = WithdrawSwap().apply(lp, tkn, user_nm, 100)
lp.summary()

Exchange ETH-TKN (LP) Reserves: ETH = 1000.0, TKN = 99900.0 Liquidity: 9994.991239989282

Notes

The mechanism is: perform 50/50 withdrawal sized to the target → swap remaining 50% → return the consolidated target token.
The realized output is less than the target by approximately one swap fee (30 bps on V2; the configured tier on V3) — that’s the cost of consolidating to a single side.