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Engineering Python · Language Basics

Expressions and Operators

In Engineering Python because every formula in a lab is an expression — arithmetic, comparison and string ops are the calculators you will reuse.

Expressions compute values. Arithmetic operators combine numbers; comparisons yield booleans; some operators work on strings too. Parentheses control order when precedence is unclear.

  • Engineering Python
  • Easy level
  • 4 concepts

1Arithmetic operators

`+ - * /` do the usual arithmetic. `/` always yields a float in Python 3. `//` is floor division; `%` is remainder; `**` is power.

Figure. / always yields a float. // is floor division; % is remainder; ** is power.

Division flavours

print(7 / 2)
print(7 // 2)
print(7 % 2)
print(2 ** 3)
What is `7 // 2` in Python 3?
  1. 3
  2. 3.5
  3. 1

Floor division discards the fractional part toward -inf for positives here yielding 3.

2Comparisons are booleans

`== != < <= > >=` compare values and return `True` or `False`. These feed `if` later.

Figure. Comparisons return True or False. These booleans later feed if.

Takeaway

  1. Idea`== != < <= > >=` compare values and return `True` or `False`. These feed `if` later.

Compare

print(3 < 5)
print(3 == 5)
What is the boolean evaluation of the expression (5 > 3) and (2 == 4)?
  1. True, because at least one operand is truthy
  2. None, because comparison operators return void
  3. An error, because parentheses cannot group logical expressions
  4. False, because the right operand 2 == 4 evaluates to false

In an and conjunction, both sides must be True. Here (True and False) evaluates to False.

3String operators

`+` concatenates strings. `*` repeats a string. You cannot add a number to a string without casting.

Figure. + concatenates strings. * repeats a string. You cannot add a number to a string without casting.

Takeaway

  1. Idea`+` concatenates strings. `*` repeats a string. You cannot add a number to a string without casting.

Concatenate and repeat

print("lab-" + "01")
print("na" * 3)

4Lab: evaluate expressions

Compute a small formula and print it so the check can see the result.

Figure. Parentheses make the intended order obvious. (3 + 4) * 2 prints 14.

Takeaway

  1. IdeaCompute a small formula and print it so the check can see the result.

Coding lab. Evaluate a formula runs in the app, with checks on your output.

Notes

  • In Engineering Python because every formula in a lab is an expression — arithmetic, comparison and string ops are the calculators you will reuse.
  • `+ - * /` do the usual arithmetic. `/` always yields a float in Python 3. `//` is floor division; `%` is remainder; `**` is power.
  • `== != < <= > >=` compare values and return `True` or `False`. These feed `if` later.

Exam traps & shortcuts

  • Run one cell at a time and read stdout before changing more lines.
  • Names are labels for values; rebinding a name does not rewrite old prints.

Recap

Expressions compute; comparisons yield bools; string + concatenates.

Arithmetic operators
`+ - * /` do the usual arithmetic. `/` always yields a float in Python 3. `//` is floor division; `%` is remainder; `**` is power.
Comparisons are booleans
`== != < <= > >=` compare values and return `True` or `False`. These feed `if` later.
String operators
`+` concatenates strings. `*` repeats a string. You cannot add a number to a string without casting.
Lab: evaluate expressions
Compute a small formula and print it so the check can see the result.

Practise Expressions and Operators

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