Exception Handling Performance

Do Not Use Exceptions for Flow Control

# Bad
for x in data:
    try:
        result.append(d[x])
    except KeyError:
        pass

# Good
get = d.get
for x in data:
    val = get(x)
    if val is not None:
        result.append(val)

Exception Handling Compiles Fine

try/except blocks themselves compile well. The overhead is in raising exceptions frequently.