Lecture 2 – Names


from operator import add, mul
from operator import *

Though you can import everything from math, or 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)
>>> max = 7
>>> max(4, 5)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object is not callable

How to get “max” back?

__builtins__.max(3, 4)
max = __builtins__.max


del max

f is max, g id min, max is min

Types of Expressions

Primitive expressions

Expression Type
2 number/numeral
'hello' string
add name

Call expressions

Environment Diagrams


  • Within a frame, a name CANNOT be repeated
  • Everytime 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

Defining Functions

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>

Function signature indicates how many arguments a function takes.

Function body defines the computation performed when the function is applied.

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I'm Bobby Yan, a programmer, music lover, researcher, and a third-year undergraduate student at UC Berkeley majoring in Electrical Engineering and Computer Science. I am currently doing research on robotics, planning, and systems for machine learning at RISELab. In the past, I built IB Notes, a website with useful and concise study guides and notes for IB, and Spanish Vocab Builder, an iOS app to help Spanish learners. See my résumé for more details.

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