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If you simply need to iterate trough the result, you can use the equivalent "),a("code",[t._v(".iterkeys()")]),t._v(", "),a("code",[t._v(".itervalues()")]),t._v(" and "),a("code",[t._v(".iteritems()")]),t._v(".")]),t._v(" "),a("p",[t._v("The difference between "),a("code",[t._v(".keys()")]),t._v(" and "),a("code",[t._v(".iterkeys()")]),t._v(", "),a("code",[t._v(".values()")]),t._v(" and "),a("code",[t._v(".itervalues()")]),t._v(", "),a("code",[t._v(".items()")]),t._v(" and "),a("code",[t._v(".iteritems()")]),t._v(" is that the "),a("code",[t._v("iter*")]),t._v(" methods are generators. Thus, the elements within the dictionary are yielded one by one as they are evaluated. When a "),a("code",[t._v("list")]),t._v(" object is returned, all of the elements are packed into a list and then returned for further evaluation.")]),t._v(" "),a("blockquote"),t._v(" "),a("p",[t._v("Note also that in Python 3, Order of items printed in the above manner does not follow any order.")]),t._v(" "),a("h2",{attrs:{id:"the-pass-statement"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#the-pass-statement"}},[t._v("#")]),t._v(" The Pass Statement")]),t._v(" "),a("p",[a("code",[t._v("pass")]),t._v(" is a null statement for when a statement is required by Python syntax (such as within the body of a "),a("code",[t._v("for")]),t._v(" or "),a("code",[t._v("while")]),t._v(" loop), but no action is required or desired by the programmer. This can be useful as a placeholder for code that is yet to be written.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("for")]),t._v(" x "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("in")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token builtin"}},[t._v("range")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("pass")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("#we don't want to do anything, or are not ready to do anything here, so we'll pass")]),t._v("\n\n")])])]),a("p",[t._v("In this example, nothing will happen. The "),a("code",[t._v("for")]),t._v(" loop will complete without error, but no commands or code will be actioned. "),a("code",[t._v("pass")]),t._v(" allows us to run our code successfully without having all commands and action fully implemented.")]),t._v(" "),a("p",[t._v("Similarly, "),a("code",[t._v("pass")]),t._v(" can be used in "),a("code",[t._v("while")]),t._v(" loops, as well as in selections and function definitions etc.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("while")]),t._v(" x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("==")]),t._v(" y"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("pass")]),t._v("\n\n")])])]),a("h2",{attrs:{id:"while-loop"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#while-loop"}},[t._v("#")]),t._v(" While Loop")]),t._v(" "),a("p",[t._v("A "),a("code",[t._v("while")]),t._v(" loop will cause the loop statements to be executed until the loop condition is "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/python/1111/conditionals/8719/truth-values#t=201607241816416765906",target:"_blank",rel:"noopener noreferrer"}},[t._v("falsey"),a("OutboundLink")],1),t._v(". The following code will execute the loop statements a total of 4 times.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),t._v(" \n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("while")]),t._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("4")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("#loop statements")]),t._v("\n    i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),t._v("\n\n")])])]),a("p",[t._v("While the above loop can easily be translated into a more elegant "),a("code",[t._v("for")]),t._v(" loop, "),a("code",[t._v("while")]),t._v(" loops are useful for checking if some condition has been met. The following loop will continue to execute until "),a("code",[t._v("myObject")]),t._v(" is ready.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("myObject "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" anObject"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("while")]),t._v(" myObject"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("isNotReady"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n    myObject"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("tryToGetReady"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n\n")])])]),a("p",[a("code",[t._v("while")]),t._v(" loops can also run without a condition by using numbers (complex or real) or "),a("code",[t._v("True")]),t._v(":")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("import")]),t._v(" cmath\n\ncomplex_num "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" cmath"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("sqrt"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("while")]),t._v(" complex_num"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("      "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# You can also replace complex_num with any number, True or a value of any type")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("complex_num"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("   "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Prints 1j forever")]),t._v("\n\n")])])]),a("p",[t._v("If the condition is always true the while loop will run forever (infinite loop) if it is not terminated by a break or return statement or an exception.")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("while")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("True")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Infinite loop"')]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Infinite loop")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Infinite loop")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# Infinite loop")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# ...")]),t._v("\n\n")])])]),a("h2",{attrs:{id:"iterating-different-portion-of-a-list-with-different-step-size"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#iterating-different-portion-of-a-list-with-different-step-size"}},[t._v("#")]),t._v(" Iterating different portion of a list with different step size")]),t._v(" "),a("p",[t._v("Suppose you have a long list of elements and you are only interested in every other element of the list. Perhaps you only want to examine the first or last elements,  or a specific range of entries in your list. Python has strong indexing built-in capabilities. Here are some examples of how to achieve these scenarios.")]),t._v(" "),a("p",[t._v("Here's a simple list that will be used throughout the examples:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[t._v("lst "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'alpha'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'bravo'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'charlie'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'delta'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v("'echo'")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v("\n\n")])])]),a("h3",{attrs:{id:"iteration-over-the-whole-list"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#iteration-over-the-whole-list"}},[t._v("#")]),t._v(" Iteration over the whole list")]),t._v(" "),a("p",[t._v("To iterate over each element in the list, a "),a("code",[t._v("for")]),t._v(" loop like below can be used:")]),t._v(" "),a("div",{staticClass:"language-py extra-class"},[a("pre",{pre:!0,attrs:{class:"language-py"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("for")]),t._v(" s "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("in")]),t._v(" lst"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("print")]),t._v(" s"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(":")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("# print the first letter")]),t._v("\n\n")])])]),a("p",[t._v("The "),a("code",[t._v("for")]),t._v(" loop assigns s for each element of "),a("code",[t._v("lst")]),t._v(". 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