Warning

# Computer Lab 06, modules, namespaces, conventions

Different namespaces in Python:

• built-in namespace
• global namespace
• local namespace

Python variable scope: A scope is the portion of a program from where a namespace can be accessed directly without any prefix.

At any given moment, there are at least three nested scopes.

• Scope of the current function which has local names
• Scope of the module which has global names
• Outermost scope which has built-in names

When a reference is made inside a function, the name is searched in the local namespace, then in the global namespace and finally in the built-in namespace.

# Python program processing
# global vs local variable

count = 5
def some_method():
count = 10
print(count)
return

some_method()
print(count)

# local function shadowing a built-in one.
# You should NEVER shadow a built-in function.

def abs(val):
print("My abs() function")
if  val >= 0:
return val
else:
return -val

print(abs(-5))

main.py

import mymath

print(abs(-4))
print(mymath.abs(-4))

mymath.py

def abs(val):
print("My abs() function")
if  val >= 0:
return val
else:
return -val

## Weekly homework 06 - trigonometric functions

• Write a module mymath (file mymath.py) with 2 functions:

def cos(x):
"""Returns an approximate value of cos(x).
:param x: float, input value for which the cosine function is computed
:return: float, approximate value of cos(x)
"""

def sin(x):
"""Returns an approximate value of sin(x).
:param x: float, input value for which the sine function is computed
:return: float, approximate value of sin(x)
"""

• Use the following approximation of the sine and cosine function:

$\cos(x)=1-\frac{x^2}{2}+\frac{x^4}{24}$

$\sin(x)=x-\frac{x^3}{6}+\frac{x^5}{120}$

• Create a file/module main.py and a function called get_trig_series(lst) inside it. Implement this function so that it receives a list of floats and outputs 2 lists - a list of approximate cosines of the values in the input list and a list of approximate sines of the values in the input list. Make use of the functions in the mymath module.

    """Return lists of cosines and sines of the values in the input list
:param lst: list of floats, input values for this cos and sin functions are to be computed
:return: list of floats, approximate cosines
:return: list of floats, approximate sines

Example:
>>> cs, sn = get_trig_series([0, 0.1])
>>> print(cs, sn)
[1.0, 0.9950041666666667] [0.0, 0.09983341666666667]
"""

• Pack both 'mymath.py' and 'main.py' in a single zip file and upload it to the BRUTE system. Place both files in the root directory of the zip file, that is, do NOT zip a folder containing the .py files. Zip them directly.

### Built-in modules

import random

rng = random.Random()

# integer in range [1,6]
dice_throw = rng.randrange(1,7)

# odd integer in range [1, 199]
odd_number = rng.randrange(1,200,2)

# float drawn uniformy from a range [0, 1)
float_0_1 = rng.random()

# randomly shuffle list
shuffled_card_list = rng.shuffle(card_list)

# Simulate throwing a dice 6000 times.
# Produce a list (of length 6) with frequency of each outcome (1-6).

import math

# constants
math.pi
math.e

# square root of 9
math.sqrt(9)

math.degrees(3.14)

# sin, cos, tan, ...

# inverse trigonometric functions
math.asin(1.0)

# natural logarithm
math.log(math.e)

# base-10 logarithm
math.log10(1000)

• task 1: Evaluate $f(x)= \sin(2x) \cos(2x) - \tan(x/2)$ for $x=45$ degrees.
• task 2: Evaluate $\sqrt{x^2+y^2}$ for $x=2$, $y=100$.
• task 3: The radioisotope strontium-90 has a half-life of 38.1 years. A sample contains 100 mg of Sr-90. Calculate the remaining milligrams of Sr-90 after 100 years. $m(t)=m_o e^{- \ln(2)*t/T_{1/2}}$

## homework

Solve homework 03 - vectorlib - functions for working with vectors and submit it via Upload system in time! Check the deadline in Upload system.
Prepare for the midterm test! Its content may be based on all the topics covered so far.