my context manager was worse off than I thought :(

patcher

Original version ('pre' prints the patched callable before entering the 'with' block, and 'post' does the same inside the 'with' block):

.....pre:  <unbound method Client.build_url>
post:  <MagicMock name='build_url' id='4321796496'>
.pre:  <MagicMock name='build_url' id='4321796496'>
post:  <MagicMock name='build_url' id='4321825552'>
.pre:  <MagicMock name='build_url' id='4321825552'>
post:  <MagicMock name='build_url' id='4321871248'>
.pre:  <MagicMock name='build_url' id='4321871248'>
post:  <MagicMock name='build_url' id='4321904656'>
.pre:  <MagicMock name='build_url' id='4321904656'>
post:  <MagicMock name='build_url' id='4321938640'>
.pre:  <MagicMock name='build_url' id='4321938640'>
post:  <MagicMock name='build_url' id='4321989328'>
.pre:  <MagicMock name='build_url' id='4321989328'>
post:  <MagicMock name='build_url' id='4322023568'>
.pre:  <MagicMock name='build_url' id='4322023568'>
post:  <MagicMock name='build_url' id='4322066064'>
.pre:  <MagicMock name='build_url' id='4322066064'>
post:  <MagicMock name='build_url' id='4324340944'>

Updated version:

.....pre:  <unbound method Client.build_url>
post:  <MagicMock name='build_url' id='4321796496'>
.pre:  <unbound method Client.build_url>
post:  <MagicMock name='build_url' id='4321829584'>
.pre:  <unbound method Client.build_url>
post:  <MagicMock name='build_url' id='4321866768'>
.pre:  <unbound method Client.build_url>
post:  <MagicMock name='build_url' id='4321903952'>
.pre:  <unbound method Client.build_url>
post:  <MagicMock name='build_url' id='4321937040'>
.pre:  <unbound method Client.build_url>
post:  <MagicMock name='build_url' id='4321970576'>
.pre:  <unbound method Client.build_url>
post:  <MagicMock name='build_url' id='4322008400'>
.pre:  <unbound method Client.build_url>
post:  <MagicMock name='build_url' id='4322050448'>
.pre:  <unbound method Client.build_url>
post:  <MagicMock name='build_url' id='4322084240'>