Variables and Types

Python has a small set of built-in types. The four you will use constantly are int, float, str and bool.

A variable is a name bound to a value. You do not declare a type; the value carries its own type.

gene = "TP53"
position = 7676154
frequency = 0.51
is_pathogenic = True

print(type(gene), type(position), type(frequency), type(is_pathogenic))

Checking and converting types

type() reports a type. The type names double as conversion functions.

depth = "120"
print(type(depth))
print(int(depth) + 1)
print(float("0.51") * 2)
print(str(42) + " reads")

Conversion fails if the text is not a valid number:

value = "twelve"
try:
    print(int(value))
except ValueError as error:
    print("could not convert:", error)

Integer and float division

/ always produces a float. // discards the remainder. % gives the remainder.

print(7 / 2)
print(7 // 2)
print(7 % 2)

This matters for codon arithmetic: a coding position divided by 3 gives the codon number, and the remainder gives the position within the codon.

Task

Write describe(value). It receives a string, and must:

1. Return "int <n>" if the string converts to a whole number.
2. Return "float <f>" if it converts to a decimal number but not a whole one.
3. Return "str <value>" otherwise.

Check int before float, because int("3") succeeds and float("3") also succeeds.