FizzBuzz in Python with nested conditional expressions and a generator expression

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- By Vasudev Ram - Online Python training / SQL training / Linux training

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The FizzBuzz problem [1] is known to those who test/interview programming candidates, as one simple way to filter out unsuitable people early. One keeps on coming across mentions of it on tech sites.

Here is a way of doing FizzBuzz in Python, not the most obvious way (which would be to use a for loop with an if/elif/else statement in it - although, of course, other ways are possible too). Instead, this way uses Python's language feature of conditional expressions:

# Fizzbuzz version using nested Python conditional expressions:
# Author: Vasudev Ram
# Web site: https://vasudevram.github.io
# Blog: https://jugad2.blogspot.com
# Twitter: https://mobile.twitter.com/vasudevram

for i in range(1, 101):
    print "FizzBuzz" if i % 15 == 0 else "Buzz" if i % 5 == 0 \
    else "Fizz" if i % 3 == 0 else str(i),

Output (formatted a bit to fit on the screen):

$ python fizzbuzz_w_cond_expr.py
1 2 Fizz 4 Buzz Fizz 7 8 Fizz Buzz 11 Fizz 13 14 FizzBuzz \
16 17 Fizz 19 Buzz Fizz 22 23 Fizz Buzz 26 Fizz 28 29 FizzBuzz \
31 32 Fizz 34 Buzz Fizz 37 38 Fizz Buzz 41 Fizz 43 44 FizzBuzz \
46 47 Fizz 49 Buzz Fizz 52 53 Fizz Buzz 56 Fizz 58 59 FizzBuzz \
61 62 Fizz 64 Buzz Fizz 67 68 Fizz Buzz 71 Fizz 73 74 FizzBuzz \
76 77 Fizz 79 Buzz Fizz 82 83 Fizz Buzz 86 Fizz 88 89 FizzBuzz \
91 92 Fizz 94 Buzz Fizz 97 98 Fizz Buzz

Here's another use of such conditional expressions:

Using nested conditional expressions to classify characters

Here is another Fizzbuzz version that uses both nested Python conditional expressions and a generator expression (again, formatted):

# FizzBuzz with a Python nested conditional expression and 
# a generator expression.
# Author: Vasudev Ram
# Web site: https://vasudevram.github.io
# Blog: https://jugad2.blogspot.com
# Twitter: https://mobile.twitter.com/vasudevram

print(" ".join("FizzBuzz" if i % 15 == 0 else "Buzz" if i % 5 == 0 else "Fizz" if i % 3 == 0 \
else str(i) for i in range(1, 101)))

It gives the same output as the earlier version above.

What's the subtle aspect of the FizzBuzz problem that can trip up a naive candidate?

The post by Jeff Atwood about FizzBuzz (below) is interesting.

- Enjoy.

[1] References:

Fizz Buzz (Wikipedia)

Jeff Atwood (2007-02-26): Why Can't Programmers.. Program?

Imran Ghory (2007-01-24): "Using FizzBuzz to Find Developers who Grok Coding."

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- Vasudev Ram - Online Python training and consulting

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Using nested conditional expressions to classify characters

By Vasudev Ram

While writing some Python code, I happened to use a conditional expression, a Python language feature.

Conditional expressions are expressions (not statements) that have if/else clauses inside them, and they evaluate to either one of two values (in the basic case), depending on the value of a boolean condition. For example:

for n in range(4):
    print n, 'is odd' if n % 2 == 1 else 'is even'
0 is even
1 is odd
2 is even
3 is odd

Here, the conditional expression is this part of the print statement above:

'is odd' if n % 2 == 1 else 'is even'

This expression evaluates to 'is odd' if the condition after the if is True, and evaluates to 'is even' otherwise. So it evaluates to a string in either case, and that string gets printed (after the value of n).

Excerpt from the section about conditional expressions in the Python Language Reference:

[
conditional_expression ::= or_test ["if" or_test "else" expression]
expression ::= conditional_expression | lambda_expr

Conditional expressions (sometimes called a “ternary operator”) have the lowest priority of all Python operations.

The expression x if C else y first evaluates the condition, C (not x); if C is true, x is evaluated and its value is returned; otherwise, y is evaluated and its value is returned.
]

You can see that the definition of conditional_expression is recursive, since it is partly defined in terms of itself (via the definition of expression).

This implies that you can have recursive or nested conditional expressions.

Also, since the syntax of the Python return statement is:

return [ expression_list ]

(where expression_list means one or more expressions, separated by commas, it follows that we can use a nested conditional expression in a return statement (because a nested conditional expresssion is an expression).

Here is a small program to demonstrate that:

'''
File: return_with_nested_cond_exprs.py 
Purpose: Demonstrate nested conditional expressions used in a return statement, 
to classify letters in a string as lowercase, uppercase or neither.
Also demonstrates doing the same task without a function and a return, 
using a lambda and map instead.
Author: Vasudev Ram
Copyright 2017 Vasudev Ram
Web site: https://vasudevram.github.io
Blog: https://jugad2.blogspot.com
'''

from __future__ import print_function
from string import lowercase, uppercase

# Use return with nested conditional expressions inside a function, 
# to classify characters in a string as lowercase, uppercase or neither:
def classify_char(ch):
    return ch + ': ' + ('lowercase' if ch in lowercase else \
    'uppercase' if ch in uppercase else 'neither')

print("Classify using a function:")
for ch in 'AaBbCc12+-':
    print(classify_char(ch))

print()

# Do it using map and lambda instead of def and for:
print("Classify using map and lambda:")

print('\n'.join(map(lambda ch: ch + ': ' + ('lowercase' if ch in lowercase else 
'uppercase' if ch in uppercase else 'neither'), 'AaBbCc12+-')))

Running it with:

$ python return_with_nested_cond_exprs.py

gives this output:

Classify using a function:
A: uppercase
a: lowercase
B: uppercase
b: lowercase
C: uppercase
c: lowercase
1: neither
2: neither
+: neither
-: neither

Classify using map and lambda:
A: uppercase
a: lowercase
B: uppercase
b: lowercase
C: uppercase
c: lowercase
1: neither
2: neither
+: neither
-: neither

As you can see from the code and the output, I also used that same nested conditional expression in a lambda function, along with map, to do the same task in a more functional style
.

- Vasudev Ram - Online Python training and consulting

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