Can't identify syntax error? Also, need using raw_input with list

Question

I'm trying to develop a simple Python program to calculate the formula mass of a compound. I'm facing 2 issues:

There's apparently a syntax error with 'b' but I don't know what it is. Here is what I've done so far:

def FormulaMass():
    H = 1
    He = 4
    Li = 7
    Be = 9
    B = 11
    C = 12
    N = 14
    O = 16
    F = 19
    Ne = 20
    Na = 23
    Mg = 24
    Al = 27
    Si = 28
    P = 31
    S = 32
    Cl = 35.5
    Ar = 40
    K = 39
    Ca = 40
    Sc = 45
    Ti = 48
    V = 51
    Cr = 52
    Mn = 55
    Fe = 56
    Co = 59
    Ni = 59
    Cu = 63.5
    Zn = 65
    Ga = 70
    Ge = 73
    As = 75
    Se = 79
    Br = 80
    Rb = 85.5
    Sr = 88
    Y = 89
    Zr = 91
    Nb = 93
    Mo = 96
    Tc = 98
    Ru = 101
    Rh = 103
    Pd = 106.5
    Ag = 108
    Cd = 112.5
    In = 115
    Sn = 119
    Sb = 122
    Te = 128
    I =127
    Xe = 131
    Cs = 133
    Ba = 137
    La = 139
    Ce = 140
    Pr = 141
    Nd = 144
    Pm = 145
    Sm = 150
    Eu = 152
    Gd = 157
    Tb = 159
    Dy = 162.5
    Ho = 165
    Er = 167
    Tm = 169
    Yb = 173
    Lu = 175
    Hf = 178.5
    Ta = 181
    W = 184
    Re = 186
    Os = 190
    Ir = 192
    Pt = 195
    Au = 197
    Hg = 201
    Tl = 204
    Pb = 207
    Bi = 209
    Po = 209
    At = 210
    Rn = 222
    Fr = 223
    Ra = 226
    Ac = 227
    Th = 232
    Pa = 231
    U = 238
    Np = 237
    Pu = 244
    Am = 243
    Cm = 247
    Bk = 247
    Cf = 251
    Es = 252
    Fm = 257
    Md = 258
    No = 259
    Rf = 261
    Db = 262
    Sg = 266
    Bh = 264
    Hs = 277
    Mt = 268
    Ds = 271
    Rg = 272
    Uub = 285
    Uut = 284
    Uuq = 289
    Uup = 288
    Uuh = 292
    Uuo = 294

    element = [H, He, Li, Be, B. C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, I, Xe, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, Po, At, Rn, Fr, Ra, Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, Uub, Uut, Uuq, Uup, Uuh, Uuo]

    a = raw_input('Which' + str(element) + '?')
    b = float(raw_input('How many moles?'))
    c = str(raw_input('Is that all [Y/N]?'))


    while c == 'N':
        print

'a' doesn't actually come up when running the code it just immediately identifies this syntax error in 'b'.

What I'm trying to do with 'a' is to allow the user to input a constant from the list 'element' so that the mass (depending on the number of moles can be calculated). Now one potential problem I see is that I'm not sure how to allow users to input different elements with different numbers of moles without creating endless constants (e.g. a, b ,c...).

The aim is to add a*b at the end to find the mass but is there a way to make multiple a's and b's so in theory users could have a*b + a1*b1...

PS Sorry for not putting in my code properly it would take too long for me to put 4 indents after each line :/

To get the formatting right, simply paste the raw code into the edit box, select it, and then click the button which looks like two braces {} (or hit control-K). That will tell SO that you want the selected region of text treated as a code sample. — DSM
– DSM, Commented Sep 27, 2013 at 15:04
your print is incomplete and You can write: raw_input('Which' + str(element) + '?') as raw_input('Which' + ', '.join(element) + '?') — Grijesh Chauhan
– Grijesh Chauhan, Commented Sep 27, 2013 at 15:06

Michael0x2a · Accepted Answer · 2013-09-28 06:57:59Z

3

In the element list, you've done Be, B. C, N. Notice how you used a period after the 'B' rather then using a comma.

What Python is thinking that you're doing is doing B.C -- you have some sort of object named B, and are trying to get the attribute C on it. Hence the error message -- B, an integer, has no attribute named C.

There are also a few potential issues with your code. As one commentator noted, your print statement is incomplete.

I'm also assuming that you want the user to enter a given element (such as 'Ne'), then find the mass of that atom (20), then do some manipulation there.

In that case, you probably want to restructure your code so that it uses a dict and looks something like this:

def FormulaMass():
    elements = {
        'H': 1,
        'He':4, 
         # ... etc
        'Uuo': 294
    }

    element = raw_input('Which element? ')
    mass = elements[element]

    print mass
    # add math here

# Run function:
FormulaMass()

edited Sep 28, 2013 at 6:57

answered Sep 27, 2013 at 15:10

Michael0x2a

65.5k32 gold badges189 silver badges241 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

DSM Over a year ago

Even though this was a little slow :^), I'm going to delete mine in favour of it because you beat me to the suggestion to use a real data structure. I'd probably even put the element table in a flat user-readable format and then construct a dict from that.

Jonathan Lahdo Over a year ago

@Michael0x2a Thank you, I've never known about the dict function before so that was useful. However, when I run the code that you just posted nothing happens and I'm not sure why :/

Michael0x2a Over a year ago

@JonathanLahdo -- Did you make sure to call the function somewhere? (You have the line FormulaMass() somewhere in your code). Also, the code I posted contains no print statements, so it won't really do anything besides prompting for which element you want. (I tweaked my answer a bit to make it clearer what I mean)

Jonathan Lahdo Over a year ago

@Michael0x2a No I didn't, stupid mistake on my behalf :3 Thanks for editing your answer to make it clearer.

Collectives™ on Stack Overflow

Can't identify syntax error? Also, need using raw_input with list

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related