from operator import add, mul from operator import *
Though you can import everything from
operator, it’s more common to specify. Thus,
from math import pi, sin, cos
Binding two names at once
area, circ = pi * radius * radius, 2 * pi * radius
We can bind the build-in function names to values
>>> max(3, 4) 4 >>> max = 7 >>> max(4, 5) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'int' object is not callable
Now that we’ve reassigned our very useful
max function to just a number, we could get it back with:
__builtins__.max(3, 4) max = __builtins__.max
or, more simply,
An expression describes a computation and evaluates to a value.
A primitive expression is a single evaluation step. You either look up the value of a name or take the literal value. Some examples are:
A call expression makes one or more function calls, for example:
- Within a frame, a name cannot be repeated
- Every time a user-defined function is called, a local frame is created
Looking up Names in Environments
The current environment is either:
- the global frame alone, or
- a local frame, followed by the global frame
Assignment is a simple means of abstraction, by binding names to values
Function definition is a more powerful means of abstraction, by binding names to expressions
def <name>(<formal parameters>): return <return expression>
A function signature indicates how many arguments a function takes.
A function body defines the computation performed when the function is applied.
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