{"id":5147,"date":"2022-02-26T13:23:11","date_gmt":"2022-02-26T12:23:11","guid":{"rendered":"http:\/\/miro.borodziuk.eu\/?p=5147"},"modified":"2025-05-05T18:07:45","modified_gmt":"2025-05-05T16:07:45","slug":"conditionals","status":"publish","type":"post","link":"http:\/\/miro.borodziuk.eu\/index.php\/2022\/02\/26\/conditionals\/","title":{"rendered":"Conditionals"},"content":{"rendered":"
\n

1. The comparison<\/strong> (otherwise known as relational<\/i>) operators are used to compare values. The table below illustrates how the comparison operators work, assuming that x = 0<\/code>, y = 1<\/code>, and z = 0<\/code>:<\/p>\n<\/div>\n

<\/p>\n

\n\n\n\n\n\n\n\n\n\n
Operator<\/th>\nDescription<\/th>\nExample<\/th>\n<\/tr>\n
==<\/code><\/td>\nreturns True<\/code> if operands’ values are equal, and False<\/code> otherwise<\/td>\n<\/td>\n<\/tr>\n
!=<\/code><\/td>\nreturns True<\/code> if operands’ values are not equal, and False<\/code> otherwise<\/td>\n\n
\n
\n
x<\/span> !=<\/span> y<\/span> # True<\/span><\/code><\/div>\n
x<\/span> !=<\/span> z<\/span> # False<\/span><\/code><\/div>\n
<\/div>\n<\/div>\n<\/div>\n<\/td>\n<\/tr>\n
><\/code><\/td>\nTrue<\/code> if the left operand’s value is greater than the right operand’s value, and False<\/code> otherwise<\/td>\n\n
\n
\n
x<\/span> ><\/span> y<\/span> # False<\/span><\/code><\/div>\n
y<\/span> ><\/span> z<\/span> # True<\/span><\/code><\/div>\n
<\/div>\n<\/div>\n<\/div>\n<\/td>\n<\/tr>\n
<<\/code><\/td>\nTrue<\/code> if the left operand’s value is less than the right operand’s value, and False<\/code> otherwise<\/td>\n\n
\n
\n
x<\/span> <<\/span> y<\/span> # True<\/span><\/code><\/div>\n
y<\/span> <<\/span> z<\/span> # False<\/span><\/code><\/div>\n
<\/div>\n<\/div>\n<\/div>\n<\/td>\n<\/tr>\n
\u2265<\/code><\/td>\nTrue<\/code> if the left operand’s value is greater than or equal to the right operand’s value, and False<\/code> otherwise<\/td>\n\n
\n
\n
x<\/span> >=<\/span> y<\/span> # False<\/span><\/code><\/div>\n
x<\/span> >=<\/span> z<\/span> # True<\/span><\/code><\/div>\n
y<\/span> >=<\/span> z<\/span> # True<\/span><\/code><\/div>\n
<\/div>\n<\/div>\n<\/div>\n<\/td>\n<\/tr>\n
\u2264<\/code><\/td>\nTrue<\/code> if the left operand’s value is less than or equal to the right operand’s value, and False<\/code> otherwise<\/td>\n\n
\n
\n
x<\/span> <=<\/span> y<\/span> # True<\/span><\/code><\/div>\n
x<\/span> <=<\/span> z<\/span> # True<\/span><\/code><\/div>\n
y<\/span> <=<\/span> z<\/span> # False<\/span><\/code><\/div>\n
<\/div>\n<\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

2. When you want to execute some code only if a certain condition is met, you can use a conditional statement<\/strong>:<\/p>\n

    \n
  • \n
      \n
    • a single if<\/code> statement, e.g.:<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
      \n
      \n
      x = 10\r\n\r\nif x == 10: # condition\r\n   print(\"x is equal to 10\") # Executed if the condition is True.<\/pre>\n<\/div>\n<\/div>\n
        \n
      • \n
          \n
        • a series of if<\/code> statements, e.g.:<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
          \n
          \n
          x = 10\r\n\r\nif x > 5: # condition one\r\n   print(\"x is greater than 5\") # Executed if condition one is True.\r\n\r\nif x < 10: # condition two\r\n   print(\"x is less than 10\") # Executed if condition two is True.\r\n\r\nif x == 10: # condition three\r\n   print(\"x is equal to 10\") # Executed if condition three is True.<\/pre>\n<\/div>\n<\/div>\n
          Each if<\/code> statement is tested separately.<\/p>\n<\/div>\n
          \n
            \n
          • \n
              \n
            • an if-else<\/code> statement, e.g.:<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
              \n
              \n
              x = 10\r\n\r\nif x < 10: # Condition\r\n  print(\"x is less than 10\") # Executed if the condition is True.\r\n\r\nelse:\r\n  print(\"x is greater than or equal to 10\") # Executed if the condition is False.<\/pre>\n<\/div>\n<\/div>\n
                \n
              • \n
                  \n
                • a series of if<\/code> statements followed by an else<\/code>, e.g.:<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
                  \n
                  \n
                  x = 10\r\n\r\nif x > 5: # True\r\nprint(\"x > 5\")\r\n\r\nif x > 8: # True\r\n  print(\"x > 8\")\r\n\r\nif x > 10: # False\r\n  print(\"x > 10\")\r\n\r\nelse:\r\n  print(\"else will be executed\")<\/pre>\n
                  Each if<\/code> is tested separately. The body of else<\/code> is executed if the last if<\/code> is False<\/code>.<\/p>\n<\/div>\n<\/div>\n
                    \n
                  • \n
                      \n
                    • The if-elif-else<\/code> statement, e.g.:<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
                      \n
                      \n
                      x = 10\r\n\r\nif x == 10: # True\r\n   print(\"x == 10\")\r\n\r\nif x > 15: # False\r\n   print(\"x > 15\")\r\n\r\nelif x > 10: # False\r\n   print(\"x > 10\")\r\n\r\nelif x > 5: # True\r\n   print(\"x > 5\")\r\n\r\nelse:\r\nprint(\"else will not be executed\")<\/pre>\n
                      If the condition for if<\/code> is False<\/code>, the program checks the conditions of the subsequent elif<\/code> blocks \u2013 the first elif<\/code> block that is True<\/code> is executed. If all the conditions are False<\/code>, the else<\/code> block will be executed.<\/p>\n<\/div>\n<\/div>\n
                        \n
                      • \n
                          \n
                        • Nested conditional statements, e.g.:<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n
                          \n
                          \n
                          x = 10\r\n\r\nif x > 5: # True\r\n   if x == 6: # False\r\n      print(\"nested: x == 6\")\r\n   elif x == 10: # True\r\n      print(\"nested: x == 10\")\r\n   else:\r\n      print(\"nested: else\")\r\nelse:\r\n   print(\"else\")<\/pre>\n<\/div>\n<\/div>\n<\/div>\n
                           <\/p>\n
                           <\/p>\n
                          Exercise 1<\/strong><\/p>\n
                          What is the output of the following snippet?<\/p>\n
                          x = 5\r\ny = 10\r\nz = 8\r\n\r\nprint(x > y)\r\nprint(y > z)<\/pre>\n
                           <\/p>\n
                          False
                          \nTrue<\/code><\/div>\n
                           <\/p>\n
                          Exercise 2<\/strong><\/p>\n
                          What is the output of the following snippet?<\/p>\n
                          x, y, z = 5, 10, 8\r\n\r\nprint(x > z)\r\nprint((y - 5) == x)<\/pre>\n
                           <\/p>\n
                          False
                          \nTrue<\/code><\/div>\n
                           <\/p>\n
                          Exercise 3<\/strong><\/p>\n
                          What is the output of the following snippet?<\/p>\n
                          x, y, z = 5, 10, 8\r\nx, y, z = z, y, x\r\n\r\nprint(x > z)\r\nprint((y - 5) == x)<\/pre>\n
                           <\/p>\n
                          True
                          \nFalse<\/code><\/div>\n
                           <\/p>\n
                          Exercise 4<\/strong><\/p>\n
                          What is the output of the following snippet?<\/p>\n
                          x = 10\r\n\r\nif x == 10:\r\n  print(x == 10)\r\nif x > 5:\r\n  print(x > 5)\r\n\r\nif x < 10:\r\n  print(x < 10)\r\nelse:\r\n  print(\"else\")<\/pre>\n
                           <\/p>\n
                          \n
                          True
                          \nTrue
                          \nelse<\/code><\/div>\n
                          <\/div>\n<\/div>\n
                          \n
                           <\/p>\n
                          Exercise 5<\/strong><\/p>\n
                          What is the output of the following snippet?<\/p>\n
                          x = \"1\"\r\n\r\nif x == 1:\r\n  print(\"one\")\r\nelif x == \"1\":\r\n  if int(x) > 1:\r\n    print(\"two\")\r\n  elif int(x) < 1:\r\n    print(\"three\")\r\n  else:\r\n    print(\"four\")\r\nif int(x) == 1:\r\n  print(\"five\")\r\nelse:\r\n  print(\"six\")<\/pre>\n
                           <\/p>\n<\/div>\n
                          four
                          \nfive<\/code><\/div>\n
                           <\/p>\n
                          Exercise 6<\/strong><\/p>\n
                          What is the output of the following snippet?<\/p>\n
                          x = 1\r\ny = 1.0\r\nz = \"1\"\r\n\r\nif x == y:\r\n  print(\"one\")\r\nif y == int(z):\r\n  print(\"two\")\r\nelif x == y:\r\n  print(\"three\")\r\nelse:\r\n  print(\"four\")<\/pre>\n
                           <\/p>\n
                          \n
                          one
                          \ntwo<\/code><\/div>\n<\/div>\n
                           <\/p>\n
                          Ex. 7<\/p>\n
                          What is the output of the following code snippet?<\/p>\n
                          incipit = \"It was a dark and stormy night\"\r\n\r\nif 'it' in incipit:\r\n  print('one')\r\nelif 'ht\"' in incipit:\r\n  print('two')\r\nelse:\r\n  print('three')<\/pre>\n
                           <\/p>\n
                          three<\/p>\n
                            \n
                          • The program executes the else<\/strong><\/code> statement and outputs three<\/strong><\/code> to the console.<\/li>\n
                          • The if<\/strong><\/code> condition is False<\/strong><\/code> because the lowercase substring 'it'<\/strong><\/code> is not present in incipit<\/strong><\/code>.<\/li>\n
                          • The elif<\/strong><\/code> condition is also False<\/strong><\/code>, because the substring 'ht\"'<\/strong><\/code>includes a quotation mark<\/strong> that is not part of the string contained in the incipit<\/strong><\/code> variable.<\/li>\n<\/ul>\n
                             <\/p>\n
                            Ex. 8<\/p>\n
                            \n
                            \n
                            \n
                            What is the output of the following code snippet?<\/p>\n
                            \n
                            \n
                            a = 3\r\nb = '3'\r\nc = 3.0\r\n\r\nif int(b) == a:\r\n  print('A')\r\n\r\nif a == b:\r\n  print('B')\r\n\r\nif c == a:\r\n  print('C')<\/pre>\n
                             <\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
                            \n
                            \n
                            \n
                            Correct answer<\/span><\/div>\n
                            \n
                            \n
                            \n
                            \n
                            A<\/span><\/p>\n
                            C<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
                            \n
                            <\/div>\n<\/div>\n
                            \n
                            \n
                            \n
                              \n
                            • The condition of the first<\/strong> if<\/strong><\/code> statement is True<\/strong><\/code>, because the int()<\/strong><\/code> function converts every literal integer, represented as a string, into the corresponding integer.int(b) == a <\/strong><\/code>-><\/strong> int('3') == 3 <\/strong><\/code>-><\/strong> 3 == 3 <\/strong><\/code>-><\/strong> True<\/strong><\/code>\n
                              Consequently, the program prints A<\/strong><\/code> on the screen.<\/li>\n
                            • The condition of the second<\/strong> if<\/strong><\/code> statement is False<\/strong>:a == b <\/strong><\/code>-><\/strong> 3 == '3' <\/strong><\/code>-><\/strong> False<\/strong><\/code>\n
                              (the integer 3<\/strong><\/code> cannot be equal to the string '3'<\/strong><\/code>).<\/li>\n
                            • The condition of the third<\/strong> if<\/strong><\/code> statement is True<\/strong><\/code>, since the integer 3<\/strong><\/code> is implicitly converted to float before comparison:c == a <\/strong><\/code>-><\/strong> 3.0 == 3 <\/strong><\/code>-><\/strong> 3.0 == 3.0 <\/strong><\/code>-><\/strong> True<\/strong><\/code>\n
                              The print()<\/strong><\/code> function outputs the letter C<\/strong> to console.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"
                              1. The comparison (otherwise known as relational) operators are used to compare values. The table below illustrates how the comparison operators work, assuming that x = 0, y = 1, and z = 0:<\/p>\n","protected":false},"author":2,"featured_media":5932,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[100],"tags":[],"_links":{"self":[{"href":"http:\/\/miro.borodziuk.eu\/index.php\/wp-json\/wp\/v2\/posts\/5147"}],"collection":[{"href":"http:\/\/miro.borodziuk.eu\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/miro.borodziuk.eu\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/miro.borodziuk.eu\/index.php\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/miro.borodziuk.eu\/index.php\/wp-json\/wp\/v2\/comments?post=5147"}],"version-history":[{"count":13,"href":"http:\/\/miro.borodziuk.eu\/index.php\/wp-json\/wp\/v2\/posts\/5147\/revisions"}],"predecessor-version":[{"id":5933,"href":"http:\/\/miro.borodziuk.eu\/index.php\/wp-json\/wp\/v2\/posts\/5147\/revisions\/5933"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/miro.borodziuk.eu\/index.php\/wp-json\/wp\/v2\/media\/5932"}],"wp:attachment":[{"href":"http:\/\/miro.borodziuk.eu\/index.php\/wp-json\/wp\/v2\/media?parent=5147"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/miro.borodziuk.eu\/index.php\/wp-json\/wp\/v2\/categories?post=5147"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/miro.borodziuk.eu\/index.php\/wp-json\/wp\/v2\/tags?post=5147"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}