1. INPUT through functions - Rakhmanov

[Pages:8]1. INPUT through functions

In [1]: C = input('C=?') C = float(C) F = (9./5)*C + 32 print (F)

C=?24 75.2

What is the difference between upper and lower program?

In [3]: C = float(input('C=?')) F = (9./5)*C + 32 print (F)

C=?24 75.2

EVAL function

In [6]: r = eval('1+2') r

Out[6]: 3

In [7]: a='1' b='2' c=eval(a+b) c

Out[7]: 12

In [8]: from math import sqrt r = eval('sqrt(2)') r

Out[8]: 1.4142135623730951

In [10]:

# Perimeter of Square def calculatePerimeter(l):

return 4*l

# Area of Square def calculateArea(l):

return l*l

expression = input("Type a function: ")

for l in range(1, 5): if (expression == 'calculatePerimeter(l)'): print("If length is ", l, ", Perimeter = ", eval(expression)) elif (expression == 'calculateArea(l)'): print("If length is ", l, ", Area = ", eval(expression)) else: print('Wrong Function') break

Type a function: calculateArea(l) If length is 1 , Area = 1 If length is 2 , Area = 4 If length is 3 , Area = 9 If length is 4 , Area = 16

EXEC

In [11]: program = 'a = 5\nb=10\nprint("Sum =", a+b)' exec(program)

Sum = 15

In [12]:

a = 5 b=10 print("Sum =", a+b)

Sum = 15

In [ ]:

program = input('Enter a program:') exec(program)

# [print(item) for item in [1, 2, 3]]

From String to code We need to install Scitools with: pip install scitools3

In [13]: from math import *

def f2(x): return exp(x)*sin(x)

In [14]: f2(2) Out[14]: 6.71884969742825

In [15]:

from scitools.StringFunction import StringFunction formula = 'exp(x)*sin(x)' f = StringFunction(formula)

# turn formula into function f(x)

In [16]: f(2) Out[16]: 6.71884969742825

2. Command line input

Cretae following programs and test through prompt

In [ ]:

# one input import sys C = float(sys.argv[1]) F = 9.0*C/5 + 32 print (F)

In [ ]:

import sys t = float(sys.argv[1]) v0 = float(sys.argv[2]) g = 9.81 y = v0*t - 0.5*g*t**2 print (y)

Error handling

In [18]:

C = float(input('Enter degree Celsium:')) F = 9.0*C/5 + 32 print (F)

Enter degree Celsium:5 41.0

In [19]:

try: C = float(input('Enter degree Celsium:'))

except: print ('You failed to provide Celsius degrees as input on the command line!') sys.exit(1) # abort

F = 9.0*C/5 + 32 print ('%gC is %.1fF' % (C, F))

Enter degree Celsium:we You failed to provide Celsius degrees as input on the command line!

---------------------------------------------------------------------------

ValueError

Traceback (most recent call last)

in

1 try:

----> 2

C = float(input('Enter degree Celsium:'))

3 except:

ValueError: could not convert string to float: 'we'

During handling of the above exception, another exception occurred:

NameError

Traceback (most recent call last)

in

3 except:

4

print ('You failed to provide Celsius degrees as input on the co

mmand line!')

----> 5

sys.exit(1) # abort

6

7 F = 9.0*C/5 + 32

NameError: name 'sys' is not defined

In [ ]:

try: C = float(input('Enter degree Celsium:'))

except IndexError: print ('Celsius degrees must be supplied on the command line') sys.exit(1) # abort execution

except ValueError: print ('Celsius degrees must be a pure number, not "%s"' % C) sys.exit(1)

F = 9.0*C/5 + 32 print ('%gC is %.1fF' % (C, F))

examples of Errors in python

In [23]:

data = [1.0/i for i in range(1,10)] data[we]

---------------------------------------------------------------------------

NameError

Traceback (most recent call last)

in

1 data = [1.0/i for i in range(1,10)]

----> 2 data[we]

NameError: name 'we' is not defined

In [24]: C = float('21 C')

---------------------------------------------------------------------------

ValueError

Traceback (most recent call last)

in

----> 1 C = float('21 C')

ValueError: could not convert string to float: '21 C'

In [25]:

forr d in data: return data

File "", line 1 forr d in data: ^

SyntaxError: invalid syntax

3. Interface

In [26]: import tkinter tkinter._test()

In [27]:

from tkinter import * root = Tk() C_entry = Entry(root, width=4) C_entry.pack(side='left') Cunit_label = Label(root, text='Celsius') Cunit_label.pack(side='left')

def compute(): C = float(C_entry.get()) F = (9./5)*C + 32 F_label.configure(text='%g' % F)

compute = Button(root, text=' is ', command=compute) compute.pack(side='left', padx=4)

F_label = Label(root, width=4) F_label.pack(side='left') Funit_label = Label(root, text='Fahrenheit') Funit_label.pack(side='left')

root.mainloop()

Modules

Assume I am depositing money to bank. Following are the fowmulas used to calculate annual interest.

= (1 + ) Amount to return:

0

360100

Following formulas can be derived from upper formula:

= (1 + ) 0 Initial ammount needed: = Number of days needed:

= 360 100 (( ) - 1) Rate needed:

-

ln(1l+n03600110306)0100

You can answer question like what should be initial ammount to get back so so amount? How many days it should be deposited? What should be annual rate?

In [28]: from math import log as ln def present_amount(A0, p, n):

return A0*(1 + p/(360.0*100))**n def initial_amount(A, p, n):

return A*(1 + p/(360.0*100))**(-n) def days(A0, A, p):

return ln(A/A0)/ln(1 + p/(360.0*100)) def annual_rate(A0, A, n):

return 360*100*((A/A0)**(1.0/n) - 1)

In [29]: x=initial_amount(12000,5,1000) x Out[29]: 10443.997433188539

Now assume that you have many formulas like this, and everyone in the bank need to use them. Moreover, you need to update them frequently. What is the solution?

Form a file named interest.py

In [30]: import interest

In [31]: interest.days(10450,12000,5) Out[31]: 995.8627846505938

In [33]: A0 = 10450; A = 12000; p = 5 n = interest.days(A0, A, p) years = n/365.0 print ('Money should reach your desired level after %.1f years' % years)

Money should reach your desired level after 2.7 years

In [34]: from interest import annual_rate

In [35]:

annual_rate(10450,12000,2.7*365)

Out[35]:

5.0525799686598205

Now try interest.py on command line. It won't give you anything.

We need to convert it to executable program

In [ ]:

if __name__ == '__main__': A = 2.2133983053266699 A0 = 2.0 p = 5 n = 730 print ('A=%g (%g)\nA0=%g (%.1f)\nn=%d (%d)\np=%g (%.1f)' % \ (present_amount(A0, p, n), A, initial_amount(A, p, n), A0, days(A0, A, p), n, annual_rate(A0, A, n), p))

Now it can work both as module and executable program.

Checking the module

In [36]:

from interest import * dir()

Out[36]:

['A', 'A0', 'ACTIVE', 'ALL', 'ANCHOR', 'ARC', 'BASELINE', 'BEVEL', 'BOTH', 'BOTTOM', 'BROWSE', 'BUTT', 'BaseWidget', 'BitmapImage', 'BooleanVar', 'Button', 'C', 'CASCADE',

Chapter 3.6 Review , Chapter 3.7 Exercises

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