Summary Pearson Edexcel Level 1/Level 2 GCSE

Turn over W75838A ©2024 Pearson Education Ltd. 1/1/1 Contents Introduction 4 Comments 5 Identifiers 5 Data types and conversion 5 Primitive data types 5 Conversion 5 Constants 5 Combining declaration and initialisation 5 Structured data types 5 Dimensions 5 Operators 6 Arithmetic operators 6 Relational operators 6 Logical/Boolean operators 6 Programming constructs 7 Assignment 7 Sequence 7 Blocking 7 Selection 7 Repetition 7 Iteration 7 Subprograms 8 Inputs and outputs 8 Screen and keyboard 8 Files 8 Supported subprograms 9 Built-in subprograms 9 List subprograms 10 String subprograms 11 Formatting strings 12 Library modules 13 Random library module 13 Math library module 13 Time library module 13 Turtle graphics library module 14 Tips for using turtle 14 Turtle window and drawing canvas 14 Turtle creation, visibility and movement 15 Turtle positioning and direction 15 Turtle filling shapes 15 Turtle controlling the pen 16 Turtle circles 16 Turtle colours 16 Console session 16 Code style 16 Line continuation 17 Carriage return and line feed 17 Introduction The Programming Language Subset (PLS) is a document that specifies which parts of Python 3 are required in order that the assessments can be undertaken with confidence. Students familiar with everything in this document will be able to access all parts of the Paper 2 assessment. This does not stop a teacher/student from going beyond the scope of the PLS into techniques and approaches that they may consider to be more efficient or engaging. Pearson will not go beyond the scope of the PLS when setting assessment tasks. Any student successfully using more esoteric or complex constructs or approaches not included in this document will still be awarded marks in Paper 2 if the solution is valid. The pair of symbols indicates where expressions or values need to be supplied. They are not part of the PLS. Comments Anything on a line after the character # is considered a comment. Identifiers Identifiers are any sequence of letters, digits and underscores, starting with a letter. Both upper and lower case are supported. Data types and conversion Primitive data types Variables may be explicitly assigned a data type during declaration. Variables may be implicitly assigned a data type during initialisation. Supported data types are: Data type PLS integer int real float Boolean bool character str Conversion Conversion is used to transform the data types of the contents of a variable using int(), str(), float(), bool() or list(). Conversion between any allowable types is permitted. Constants Constants are conventionally named in all uppercase characters. Combining declaration and initialisation The data type of a variable is implied when a variable is assigned a value. Structured data types A structured data type is a sequence of items, which themselves are typed. Sequences start with an index of zero. Data type Explanation PLS string A sequence of characters str array A sequence of items with the same (homogeneous) data type list record A sequence of items, usually of mixed (heterogenous) data types list Dimensions The number of dimensions supported by the PLS is two. The PLS does not support ragged data structures. Therefore, in a list of records, each record will have the same number of fields. Operators Arithmetic operators Arithmetic operator Meaning / division * multiplication ** exponentiation + addition – subtraction // integer division % modulus Relational operators Relational operator Meaning == equal to != not equal to greater than = greater than or equal to less than = less than or equal to Logical/Boolean operators Operator Meaning and both sides of the test must be true to return true or either side of the test must be true to return true not inverts Programming constructs Assignment Assignment is used to set or change the value of a variable. Sequence Every instruction comes one after the other, from the top of the file to the bottom of the file. Blocking Blocking of code segments is indicated by indentation and subprogram calls. These determine the scope and extent of variables they declare. Selection if expression: command If expression is true, then command is executed. if expression: If expression is true, then first command is command executed, otherwise second command is executed. else: command if expression: command elif expression: command If expression is true, then first command is executed, otherwise the second expression test is checked. If true, then second command is executed, otherwise third command is executed. else: command Supports multiple instances of ‘elif’. The ‘else’ is optional with the ‘elif’. Repetition Iteration for id in structure: command Executes command for each element of a data structure, in one dimension. for id in range (start, stop): command Count-controlled loop. Executes command a fixed number of times, based on the numbers generated by the range function. stop is required. start is optional. for id in range (start, stop, step): command Same as above, except that step influences the numbers generated by the range function. stop is required. start and step are optional. Subprograms def procname (): command A procedure with no parameters def procname (paramA, paramB): command A procedure with parameters def funcname (): command return (value) A function with no parameters def funcname (paramA, paramB): command return (value) A function with parameters Inputs and outputs Screen and keyboard print (item) Displays item on the screen input (prompt) Displays prompt on the screen and returns the line typed in Files The PLS supports manipulation of comma separated value text files. File operations include open, close, read, write and append. fileid = open (filename, "r") Opens file for reading for line in fileid: Reads every line, one at a time alist = fileid.readlines () Returns a list where each item is a line from the file aline = fileid.readline () Returns a line from a file. Returns an empty string on the end of the file fileid = open (filename, "w") Opens a file for writing fileid = open (filename, "a") Opens a file for appending fileid.writelines (structure) Writes structure to a file. structure is a list of strings fileid.write (aString) Writes a single string to a file fileid.close () Closes file Supported subprograms Built-in subprograms The PLS supports these built-in subprograms. Subprogram Description bool (item) Returns item converted to the equivalent Boolean value chr (integer) Returns the string which matches the Unicode value of integer. The first 128 characters of Unicode are equivalent to ASCII. float (item) Returns item converted to the equivalent real value input (prompt) Displays the content of prompt to the screen and waits for the user to type in characters followed by a new line int (item) Returns item converted to the equivalent integer value len (object) Returns the length of the object, such as a string, one-dimensional or two-dimensional data structure ord (char) Returns the integer equivalent to the Unicode string of the single character char. The first 128 characters of Unicode are equivalent to ASCII. print (item) Prints item to the display range (start, stop, step) Generates a list of numbers using step, beginning with start and up to, but not including, stop. A negative value for step goes backwards. stop is required. start and step are optional. The default value for start is zero. The default value for step is positive one. round (x, n) Rounds x to the number of n digits after the decimal (uses the 0.5 rule). The n is optional. If omitted, the function returns the nearest integer to x. str (item) Returns item converted to the equivalent string value List subprograms The PLS supports these list subprograms. Subprogram Description list.append (item) Adds item to the end of the list del list [index] Removes the item at index from list list.insert (index, item) Inserts item just before an existing one at index aList = list () aList = [] Two methods of creating a list structure. Both are empty. String subprograms The PLS supports these string subprograms. Subprogram Description len (string) Returns the length of string string.find (substring, start, end) Returns the location of the first instance of substring in the original string, reading from left to right. start is the index to begin the find. The default is zero. end is the index to stop the find. The default is the end of the string. Returns -1, if not found. string.index (substring, start, end) Returns the location of the first instance of substring found in the original string as read from left to right. Raises an exception if not found. substring is required. start and end are optional. The default value for start is zero. The default value for end is the end of the string. string.isalpha () Returns True, if all characters are alphabetic A–Z string.isalnum () Returns True, if all characters are alphabetic A–Z or digits 0–9 string.isdigit () Returns True, if all characters are digits 0–9, exponents are digits string.replace (s1, s2) Returns original string with all occurrences of s1 replaced with s2 string.split (char) Returns a list of all substrings in the original, using char as the separator string.strip (char) Returns original string with all occurrences of char removed from the front and back string.upper () Returns the original string in uppercase string.lower () Returns the original string in lowercase string.isupper () Returns True, if all characters are uppercase string.islower () Returns True, if all characters are lowercase string.format (placeholders) Formats values and puts them into the placeholders Formatting strings Output can be customised to suit the problem requirements and the user’s needs by forming string output. string.format () can be used with positional placeholders and format descriptors. Placeholders take the form: {:alignsignwidth.precisiontype} Placeholder Option Description align Left aligned. Default for most items, like text. Right aligned. Default for numbers. ^ Centre aligned. sign + Use a sign for both positive and negative numbers. − Use a sign only for negative numbers. Default for negative numbers. space Use leading spaces for positive numbers and a minus sign for negative numbers. width whole number The total width of the field. precision whole number The number of digits after the decimal. type s String. Default for strings, if not supplied. d Numbers in base 10 (denary). Default for integers, if not supplied. f Fixed-point notation. Formats a number with exactly the number of digits to the right of the decimal given by precision Here is an example: layout = "{:10} {:^5d} {:7.4f}" print (t (“Fred”, 358, 3.14159)) The * operator can be used to generate a line of repeated characters, for example: “=” * 10 will generate “==========”. Concatenation of strings is done using the + operator. String slicing is supported. myName[0:2] gives the first two characters in the variable