Adventures in Python: User-Entry Function

Adventures in Python:  User-Entry Function

The following script allows the user to enter a function, including math functions (math.sqrt, math.sin, etc).  The function is entered as string and when calculation is needed, the eval function is called. 

Script:

# Program 010:  Asking for a function - Using Eval

# To generate a table

# allow for math functions

import math

# ask for the parameters

print('Generate f(x): You can use math. functions')

print('Such as math.sqrt, math.sin, math.exp, etc.')

print('Remember the default angle measure is radians.')

print('Use math.pi for \u03C0')

# f(x) and parameters will be entered as a string

fx = input('Please enter f(x): ')

# use float for end marks

beg = input('Beginning point:  ')

end = input('Ending point:  ')

step = input('Step: ')

# use eval to evaluate the parameters, turning them into floating numbers

beg = eval(beg)

end = eval(end)

step = eval(step)

print('BEGIN')

# since a floating number with begin, end, and step may be used,

# we must use a while loop instead of a for loop

k = beg

while k<=end:

    # function evaluation

    x = k

    y = eval(fx)

    #  print the data to six decimal places

    x = round(x,6)

    y = round(y,6)

    print(x,',',y)

    print('-----')

    # use += for storage arithmetic

    k += step

# end of table

print('END')

Example:

f(x) = √(x^2 + 1) from x = 0 to x = 4, step 0.5

Result:

Generate f(x): You can use math. functions

Such as math.sqrt, math.sin, math.exp, etc.

Remember the default angle measure is radians.

Use math.pi for π

Please enter f(x): math.sqrt(x**2+1)

Beginning point:  0

Ending point:  4

Step: 0.5

BEGIN

0 , 1.0

-----

0.5 , 1.118034

-----

1.0 , 1.414214

-----

1.5 , 1.802776

-----

2.0 , 2.236068

-----

2.5 , 2.692582

-----

3.0 , 3.162278

-----

3.5 , 3.640055

-----

4.0 , 4.123106

-----

END

Pretty straight forward.  I hope you are enjoying this series on Python.  Until next time,

Eddie

This blog is property of Edward Shore, 2017

Adventures in Python: String Manipulation and Function/Derivative Table (Subroutines)

Adventures in Python:  String Manipulation and Function/Derivative Table (Subroutines)

String Manipulation

This script demonstrates several string functions:

length:  the number of characters in a string

stringname.replace(‘target string’,‘new string’):  replace a part of a string

stringname.capitalize(): capitalize the first letter of a string

stringname.split():  splits a string at its spaces

Other string functions:

stringname.lower(): makes all letters of a string to lower case

stringname.upper():  makes all letters of a string to upper case

You can join strings with the plus symbol ( + ).

The nice thing is that you won’t need to import any modules for the above string functions.

Script:

# program 008

print('Program 008: String Demo')

str1 = input('Please type some text.  ')

# input defaults to strings

# length

print('Length')

l = len(str1)

print('Length',l)

# capitalizes the first letter

print('Capitalize')

str2 = str1.capitalize()

print(str2)

# string splits at spaces

print('Split')

str3 = str1.split()

print(str3)

# replacement

str4 = str1

str4 = str4.replace('a','e')

str4 = str4.replace('u','a')

str4 = str4.replace('o','u')

str4 = str4.replace('i','o')

str4 = str4.replace('e','i')

print('Can you read this?')

print(str4)

Output:  with the “This is my demonstration.”

Program 008: String Demo

Please type some text.  This is my demonstration.

Length

Length 25

Capitalize

This is my demonstration.

Split

['This', 'is', 'my', 'demonstration.']

Can you read this?

Thos os my dimunstritoun.

Function/Derivative Table (Subroutines)

You can create user functions (subroutines) in python by the def structure.  You return results by the return command.

Script (you can enter whatever your function you like, I have imported the math module):

# Program 009 Using def and creating a table

# import math

import math

def fx(x):

     f = math.exp(-x**2/2)

     return f;

    

print('Function Table')

beg = float(input('start: '))

end = float(input('stop: '))

stp = float(input('step: '))

# loop begins

h = .00001

k = beg

print('k',':','f(x)',';','slope')

while k <= end:

     # function

     a = fx(k)

     # derivative

     b = fx(k+h)

     c = fx(k-h)

     d = (b - c)/(2 * h)

     print(k,',',a,',',d)

     print('- - - - - - - -')

     k = k + stp

           

Output (with start = 0, stop = 5, step = 1)

Function Table

start: 0

stop: 5

step: 1

k : f(x) ; slope

0.0 , 1.0 , 0.0

- - - - - - - -

1.0 , 0.6065306597126334 , -0.6065306596914066

- - - - - - - -

2.0 , 0.1353352832366127 , -0.27067056647955834

- - - - - - - -

3.0 , 0.011108996538242306 , -0.033326989618259056

- - - - - - - -

4.0 , 0.00033546262790251185 , -0.0013418505118650097

- - - - - - - -

5.0 , 3.726653172078671e-06 , -1.8633265866508763e-05

- - - - - - - -

Eddie

This blog is property of Edward Shore, 2017.