{"id":41164,"date":"2020-04-08T11:45:00","date_gmt":"2020-04-08T15:45:00","guid":{"rendered":"https:\/\/ibkrcampus.com\/?p=41164"},"modified":"2022-11-21T09:45:24","modified_gmt":"2022-11-21T14:45:24","slug":"ibkr-quant-news-python-function-tutorial-part-vi","status":"publish","type":"post","link":"https:\/\/www.interactivebrokers.com\/campus\/ibkr-quant-news\/ibkr-quant-news-python-function-tutorial-part-vi\/","title":{"rendered":"Python Function Tutorial \u2013 Part VI"},"content":{"rendered":"\n

See Part I<\/a>, Part II<\/a> <\/em>, Part III<\/a>, Part IV<\/a> and Part V<\/a> of this installment to learn more about Python functions.<\/em><\/p>\n\n\n\n

Python functions with default arguments<\/strong><\/p>\n\n\n\n

Let us say, we are writing a function that takes multiple parameters. Often, there are common values for some of these parameters. In such cases, we would like to be able to call the function without explicitly specifying every parameter. In other words, we would like some parameters to have default values that will be used when they are not specified in the function call.<\/p>\n\n\n\n

To define a python function with a default argument value, we need to assign a value to the parameter of interest while defining a function.<\/p>\n\n\n\n

\ndef power(number, pow=2):
\n “””Returns the value of number to the power of pow.”””
\n return number**pow\n<\/p>\n\n\n\n

Notice that the above python function computes the first argument to the power of the second argument. The default value of the latter is 2. So now when we call the python function power<\/code> only with a single argument, it will be assigned to the number<\/code> parameter and the return value will be obtained by squaring number<\/code>.<\/p>\n\n\n\n

\n# Calling the power function only with required argument
\nprint(power(2))
\n# Output
\n4\n<\/p>\n\n\n\n

In other words, the argument value to the second parameter pow<\/code> became optional. If we want to calculate the number for a different power, we can obviously provide a value for it and the python function will return the corresponding value.<\/p>\n\n\n\n

\n# Calling the power function with both arguments
\nprint(power(2, 5)
\n# Output
\n32\n<\/p>\n\n\n\n

We can have any number of default value parameters in a python function. Note however that they must follow non-default value parameters in the definition. Otherwise, Python will throw an error as shown below:<\/p>\n\n\n\n

\n# Calling the power function that will throw an error
\ndef power(pow=2, number):
\n “””Returns the raised number to the power of pow.”””
\n return number**pow
\n File ““, line 1
\n def power(pow=2, number):
\n ^
\nSyntaxError: non-default argument follows default argument
\n<\/p>\n\n\n\n

In the next installment, the author will discuss<\/em> Python functions with variable length arguments<\/em>.<\/p>\n\n\n\n

Visit https:\/\/www.quantinsti.com\/<\/a> for ready-to-use Python functions as applied in trading and data analysis.<\/p>\n","protected":false},"excerpt":{"rendered":"

QuantInsti demonstrates how to write Python functions with default arguments. Code along with their ready-to-use Python scripts!<\/p>\n","protected":false},"author":328,"featured_media":21196,"comment_status":"closed","ping_status":"open","sticky":true,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[343,349,338,350,341,344],"tags":[851,5615,6956,806,5614,852,595,494],"contributors-categories":[13654],"class_list":{"0":"post-41164","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-programing-languages","8":"category-python-development","9":"category-ibkr-quant-news","10":"category-quant-asia-pacific","11":"category-quant-development","12":"category-quant-regions","13":"tag-algo-trading","14":"tag-argument","15":"tag-data-analysis","16":"tag-data-science","17":"tag-lambda","18":"tag-machine-learning","19":"tag-python","20":"tag-quant","21":"contributors-categories-quantinsti"},"pp_statuses_selecting_workflow":false,"pp_workflow_action":"current","pp_status_selection":"publish","acf":[],"yoast_head":"\nPython Function Tutorial \u2013 Part VI | IBKR Quant<\/title>\n<meta name=\"description\" content=\"QuantInsti demonstrates how to write Python functions with default arguments. 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