lots of nested if statements.

[paulyche]

I'm writing a program which contains an awful lot of nested if statements. I don't know how efficient this is but it definetely makes the code less readable. Does anyone have any advice on how I can improve the following kind of code?

Apparently other languages have a switch statement which is useful here...Python seems to lack this functionality.

My Python is self-taught so I'd appreciate any outside input.

Lots of the code involves blocks of code like this:

for d1, d2, d3, d4, number in list:
  if abs(d1-a1) < D1_tol:
    if abs(d2-a2) < D2_tol:
      if abs(d3-a3) < D3_tol:
        if abs(d4) > abs(a4):
          do_something
for d1, d2, d3, d4, number in list2:
  if abs(d1-a1) < D1_tol:
    if abs(d2-a2) < D2_tol:
      if abs(d3-a3) < D3_tol:
        if abs(d4) > abs(a4):
          do_something_else
 

[dshimer]

If all those things have to be true at the same time how about "and", as a very simple example.

>>> a=1
>>> b=2
>>> c=3
>>> if a>0 and b>0 and c>0:
...     print 'y'
... else: print 'n'
... 
y
>>> a=-1
>>> if a>0 and b>0 and c>0:
...     print 'y'
... else: print 'n'
... 
n
>>> 

[paulyche]

Thanks for the reply.

I can use 'and' sometimes. However sometimes there are so many if's that they'd go off the end of the line if I used 'and' statements. That seems even less readable.

[bartonc]

Thanks for the reply.

I can use 'and' sometimes. However sometimes there are so many if's that they'd go off the end of the line if I used 'and' statements. That seems even less readable.

You can break lines in Python

if varylongname1 and varylongname2 and varylongname2 and \
    varylongname4 and varylongname5 and varylongname6:

[bvdet]

I'm writing a program which contains an awful lot of nested if statements. I don't know how efficient this is but it definetely makes the code less readable. Does anyone have any advice on how I can improve the following kind of code?

Apparently other languages have a switch statement which is useful here...Python seems to lack this functionality.

My Python is self-taught so I'd appreciate any outside input.

Lots of the code involves blocks of code like this:

for d1, d2, d3, d4, number in list:
  if abs(d1-a1) < D1_tol:
    if abs(d2-a2) < D2_tol:
      if abs(d3-a3) < D3_tol:
        if abs(d4) > abs(a4):
          do_something
for d1, d2, d3, d4, number in list2:
  if abs(d1-a1) < D1_tol:
    if abs(d2-a2) < D2_tol:
      if abs(d3-a3) < D3_tol:
        if abs(d4) > abs(a4):
          do_something_else
 

This may not be better, but is a little easier to read:

def compare_terms(*args):
    evalList = []
    for item in args:
        evalList.append(eval(item))
    return evalList
 
for d1, d2, d3, d4, number in lst:
    if False not in compare_terms('abs(d1-a1) < D1_tol',\
                                  'abs(d2-a2) < D2_tol',\
                                  'abs(d3-a3) < D3_tol',\
                                  'abs(d4) > abs(a4)'):
        do_whatever

I suggest not using 'list' for a variable name since it masks Python's built in function 'list()'.

[bartonc]

This may not be better, but is a little easier to read:

def compare_terms(*args):
    evalList = []
    for item in args:
        evalList.append(eval(item))
    return evalList
 
for d1, d2, d3, d4, number in lst:
    if False not in compare_terms('abs(d1-a1) < D1_tol',\
                                  'abs(d2-a2) < D2_tol',\
                                  'abs(d3-a3) < D3_tol',\
                                  'abs(d4) > abs(a4)'):
        do_whatever

I suggest not using 'list' for a variable name since it masks Python's built in function 'list()'.

Nice catch on a keyword being used as a variable name. Very elegant coding! Thanks BV.

[bvdet]

Nice catch on a keyword being used as a variable name. Very elegant coding! Thanks BV.

My pleasure, just glad to be here. Pushing 2,000 posts Barton? Congrats and attaboys for all your hard work!

[bvdet]

This may not be better, but is a little easier to read:

def compare_terms(*args):
    evalList = []
    for item in args:
        evalList.append(eval(item))
    return evalList
 
for d1, d2, d3, d4, number in lst:
    if False not in compare_terms('abs(d1-a1) < D1_tol',\
                                  'abs(d2-a2) < D2_tol',\
                                  'abs(d3-a3) < D3_tol',\
                                  'abs(d4) > abs(a4)'):
        do_whatever

I suggest not using 'list' for a variable name since it masks Python's built in function 'list()'.

After thinking about this again, the function is redundant:

for d1, d2, d3, d4, number in lst:
    if False not in [abs(d1-a1) < D1_tol,\
                     abs(d2-a2) < D2_tol,\
                     abs(d3-a3) < D3_tol,\
                     abs(d4) > abs(a4)
                     ]:
        do_whatever      

[paulyche]

Thanks for everyone's replies. I'll take a closer look at your suggestion bvdet and try it out.

I was only using 'list' as an example. Gedit does a good job of highlighting reserved words to keep me making too many newbie errors like that.

Once again, thanks for all your time.

[bvdet]

Thanks for everyone's replies. I'll take a closer look at your suggestion bvdet and try it out.

I was only using 'list' as an example. Gedit does a good job of highlighting reserved words to keep me making too many newbie errors like that.

Once again, thanks for all your time.

You are welcome. 'list' is not a reserved word like 'import', 'for', 'in', etc., but is a built-in function. 'list' can be used as a variable name. When the object reference to 'list' has decreased to zero, you would get the built-in function back.