▲ 1 r/CodingHelp
Help with program acknowledging a solved variable
Hey everyone, this is my first coding project and I'm having trouble with my program not recognising that it has solved for I. I was thinking that adding: if name == "I" and symbol in subs: continue. would stop it from looping but it doesn't.
Any suggestions would be appreciated.
# Beam deflection calculator
# Calculates maximum beam deflection under a uniformly distributed load
# Uses the beam deflection formula
from sympy import Symbol, solve, pprint
import math
# Allows safe math input
safe_dict = {"__builtins__": None}
safe_dict.update(vars(math))
# To track which axis is solved for if I is calculated
axis = None
# Symbol definitions
w = Symbol('w')
L = Symbol('L')
E = Symbol('E')
I = Symbol('I')
δ_max = Symbol('d')
# Beam deflection formula (simply-supported, uniform load):
expr = (5*w*L**4)/(384*E*I)
# Introduction to the program
print("\nWelcome to the Beam Deflection Calculator")
print("\nThis program calculates the maximum beam deflection under a uniformly distributed load")
# Equation setup
equation = δ_max - expr
print('\nBeam Deflection Equation:')
pprint(equation)
print('\nVariables: w, L, E, I, d(δ)')
# Define allowed variables for user input
valid_symbols = {
'w' : w,
'L' : L,
'E' : E,
'I' : I,
'd' : δ_max
}
# Define SI units for each variable
units = {
'w' : 'N/m',
'L' : 'm',
'E' : 'Pa',
'I' : 'm^4',
'd' : 'm'
}
# Unit conversions to standard factors for each variable
conversion_factors = {
'w' : {'N/m': 1, 'kN/m': 1e3, 'N/mm': 1e3, 'kN/mm': 1e6},
'L' : {'m': 1, 'mm': 1e-3, 'cm': 1e-2, 'km': 1e3},
'E' : {'Pa': 1, 'MPa': 1e6, 'GPa': 1e9, 'N/m^2': 1, 'N/mm^2': 1e6, 'N/km^2': 1e-6},
'I' : {'m^4':1, 'mm^4': 1e-12, 'cm^4': 1e-8, 'km^4': 1e12},
'd' : {'m': 1, 'mm': 1e-3, 'cm': 1e-2, 'km': 1e3}
}
# Prompt for variables & ensure a valid user input
while True:
solve_for = input('\nWhich variable would you like to solve for? (w, L, E, I, d): ').strip()
print("\nEnter values in ANY of the prompted units; results are always reported in SI units (N/m, m, Pa, m^4, m).\n")
if solve_for in valid_symbols:
break
print('Unable to solve for variable')
print('Try: w, L, E, I, d')
# Solve for symbols
var = valid_symbols[solve_for]
# Confirm choice
print(f'\nYou selected to solve for {solve_for}.')
print('Enter values for the remaining variables.\n')
subs = {}
# Get user to input values for all other variables
for name, symbol in valid_symbols.items():
if name != solve_for:
allowed_units = list(conversion_factors[name].keys())
# If user requests to solve for I:
if name == "I":
while True:
use_rect = input(
"\nDo you want to calculate I for a rectangular section? (y/n): "
).strip().lower()
if use_rect not in {"y", "n"}:
print("Please answer 'y' or 'n'.")
continue
if use_rect == "y":
while True:
axis_try = input("Calculate bending about which axis? (x/y): ").strip().lower()
if axis_try not in {"x", "y"}:
print ("Axis must be 'x' or 'y'. Try again.")
continue
axis = axis_try
try:
base = float(input("Enter base b (width) of rectangle: "))
b_unit = input("Unit for b (m, mm, cm, km): ").strip()
height = float(input('Enter height h of rectangle: '))
h_unit = input("unit for h (m, mm, cm, km): ").strip()
except Exception:
print("[!] Invalid numeric value for b or h.")
continue
conv_b = conversion_factors['L'].get(b_unit, None)
conv_h = conversion_factors['L'].get(h_unit, None)
if conv_b is None or conv_h is None:
print('[!] Invalid unit for b or h. Allowed: m, mm, cm, km')
continue
b_si = base * conv_b
h_si = height * conv_h
if axis == "x":
I_si = (1/12) * b_si * h_si**3
pretty_I = (f"Ix = (1/12) * {b_si} * {h_si}^3 = {I_si} m^4")
else:
I_si = (1/12) * h_si * b_si**3
pretty_I = (f'Iy = (1/12) * {h_si} * {b_si}^3 = {I_si} m^4')
print("\nSection dimensions (SI):")
print(f" base = {b_si} m, height = {h_si} m")
print(pretty_I)
subs[symbol] = I_si
break # User input for I finished
if name == "I" and symbol in subs:
continue
else:
# When user want's to input predetermined value for I, continue to manual entry below
break
# For manual entry of all other values
while True:
print(f'\nEnter value for {name}. Allowed units: {', '.join(allowed_units)}')
try:
value_input = input(f'Value for {name}: ').strip().lower()
value_input = value_input.replace('x', '*').replace('^', '**')
try:
value = float(eval(value_input, safe_dict))
except:
print(' [!] Invalid logarithm form. Try: e-n or *10^-n or x 10^n')
continue
unit = input(f'Unit for {name}: ').strip()
if unit not in conversion_factors[name]:
print(f' [!] Invalid unit. Allowed: {', '.join(allowed_units)}')
continue
value_si = value * conversion_factors[name][unit]
if name in ['w', 'L', 'E', 'I', 'd'] and value_si <= 0:
print(" [!] Value must be positive.")
continue
print(f' {name}: {value} {unit} → {value_si} {units[name]} (SI)')
subs[symbol] = value_si
break
except Exception:
print(' [!] Invalid input. Please enter a numeric value.')
# Solve for the variable first without substitution
solution = solve(equation, var)
# Substitute the known values and evaluate
solution = [sol.subs(subs).evalf() for sol in solution]
# keep only real, positive solutions
real_positive = [sol for sol in solution if sol.is_real and sol > 0]
print("\n=== RESULT ===")
if real_positive:
result = real_positive[0]
print(f'\n{solve_for} = {result} {units[solve_for]}')
if axis:
print(f"deflection calculated for bending about the {axis}-axis.")
else:
print(' [!] No valid physical solution found.')
exit()
if L in subs:
beam_length = subs[L]
else:
beam_length = result
max_deflection_location = beam_length / 2
print(f'\nx_max = {max_deflection_location} m (midpoint of beam)')
print('\n--- Calculation finished. Thank you for using the Beam Deflection Calculator! ---')
u/Environmental_Pen866 — 10 days ago