# Reference guide: Python concepts from module 3; Terms and definitions from Course 7, Module 3 Built-in functions The following built-in functions are commonly used in Python. ### str() Converts the input object to a string str(10) Converts the integer 10 to the string "10" ### len() Returns the number of elements in an object print(len("security")) ## Returns and displays 8, the number of characters in the string "security" ## String methods The following methods can be applied to strings in Python. ### .upper() Returns a copy of the string in all uppercase letters print("Security".upper()) Returns and displays a copy of the string "Security" as "SECURITY" ### .lower() Returns a copy of the string in all lowercase letters print("Security".lower()) Returns and displays a copy of the string "Security" as "security" ### .index() Finds the first occurrence of the input in a string and returns its location print("Security".index("c")) Finds the first occurrence of the character "c" in the string "Security" and returns and displays its index of 2 ## List methods The following methods can be applied to lists in Python. ### .insert() Adds an element in a specific position inside the list username\_list = \["elarson", "fgarcia", "tshah"\] username\_list.insert(2,"wjaffrey") Adds the element "wjaffrey" at index 2 to the username\_list; the list becomes \["elarson", "fgarcia", "wjaffrey", "tshah"\] ### .remove() Removes the first occurrence of a specific element inside a list username\_list = \["elarson", "bmoreno", "wjaffrey", "tshah"\] username\_list.remove("elarson") Removes the element "elarson" from the username\_list; the list becomes \["fgarcia", "wjaffrey", "tshah"\] ### .append() Adds input to the end of a list username\_list = \["bmoreno", "wjaffrey", "tshah"\] username\_list.append("btang") Adds the element "btang" to the end of the username\_list; the list becomes \["fgarcia", "wjaffrey", "tshah", "btang"\] ### .index() Finds the first occurrence of an element in a list and returns its index username\_list = \["bmoreno", "wjaffrey", "tshah", "btang"\] print(username\_list.index("tshah")) Finds the first occurrence of the element "tshah" in the username\_list and returns and displays its index of 2 ## Additional syntax for working with strings and lists The following syntax is useful when working with strings and lists. ### + (concatenation) Combines two strings or lists together device\_id = "IT"+"nwp12" Combines the string "IT" with the string "nwp12" and assigns the combined string of "ITnwp12" to the variable device\_id users = \["elarson", "bmoreno"\] + \["tshah", "btang"\] Combines the list \["elarson", "bmoreno"\] with the list \["tshah", "btang"\] and assigns the combined list of \["elarson", "bmoreno", "tshah", "btang"\] to the variable users ### \[\] (bracket notation) Uses indices to extract parts of a string or list print("h32rb17"\[0\]) Extracts the character at index 0, which is ("h"), from the string "h32rb17" print("h32rb17"\[0:3\]) Extracts the slice \[0:3\], which is ("h32"), from the string "h32rb17"; the first index in the slice (0) is included in the slice but the second index in the slice (3) is excluded username\_list = \["elarson", "fgarcia", "tshah"\] print(username\_list\[2\]) Extracts the element at index 2, which is ("tshah"), from the username\_list ## Regular expressions The following re module function and regular expression symbols are useful when searching for patterns in strings. ### re.findall() Returns a list of matches to a regular expression import re re.findall("a53", "a53-32c .E") Returns a list of matches to the regular expression pattern "a53" in the string "a53-32c .E"; returns the list \["a53"\] ### \\w Matches with any alphanumeric character; also matches with the underscore (\_) import re re.findall("\\w", "a53-32c .E") Returns a list of matches to the regular expression pattern "\\w" in the string "a53-32c .E"; matches to any alphanumeric character and returns the list \["a", "5", "3", "3", "2", "c", "E"\] ### . Matches to all characters, including symbols import re re.findall(".", "a53-32c .E") Returns a list of matches to the regular expression pattern "." in the string "a53-32c .E"; matches to all characters and returns the list \["a", "5", "3", "-", "3", "2", "c", " ", ".", "E"\] ### \\d Matches to all single digits import re re.findall("\\d", "a53-32c .E") Returns a list of matches to the regular expression pattern "\\d" in the string "a53-32c .E"; matches to all single digits and returns the list \["5", "3", "3", "2"\] ### \\s Matches to all single spaces import re re.findall("\\d", "a53-32c .E") Returns a list of matches to the regular expression pattern "\\s" in the string "a53-32c .E"; matches to all single spaces and returns the list \[" "\] ### \\. Matches to the period character import re re.findall("\\.", "a53-32c .E") Returns a list of matches to the regular expression pattern "\\." in the string "a53-32c .E"; matches to all instances of the period character and returns the list \["."\] ### + Represents one or more occurrences of a specific character import re re.findall("\\w+", "a53-32c .E") Returns a list of matches to the regular expression pattern "\\w+" in the string "a53-32c .E"; matches to one or more occurrences of any alphanumeric character and returns the list \["a53", "32c", "E"\] ### \* Represents, zero, one or more occurrences of a specific character import re re.findall("\\w\*", "a53-32c .E") Returns a list of matches to the regular expression pattern "\\w\*" in the string "a53-32c .E"; matches to one or more occurrences of any alphanumeric character and returns the list \["a53", " ", "32c", " ", " ", "E"\] ### { } Represents a specified number of occurrences of a specific character; the number is specified within the curly brackets import re re.findall("\\w{3}", "a53-32c .E") Returns a list of matches to the regular expression pattern "\\w{3}" in the string "a53-32c .E"; matches to exactly three occurrences of any alphanumeric character and returns the list \["a53","32c"\] --- # Glossary terms from module 3 **Algorithm:** A set of rules that solve a problem **Bracket notation:** The indices placed in square brackets **Debugging:** The practice of identifying and fixing errors in code **Immutable:** An object that cannot be changed after it is created and assigned a value **Index:** A number assigned to every element in a sequence that indicates its position **List concatenation:** The concept of combining two lists into one by placing the elements of the second list directly after the elements of the first list **List data:** Data structure that consists of a collection of data in sequential form **Method:** A function that belongs to a specific data type **Regular expression (regex):** A sequence of characters that forms a pattern **String concatenation:** The process of joining two strings together **String data:** Data consisting of an ordered sequence of characters **Substring:** A continuous sequence of characters within a string