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Intro. to Computing Name:___________________ 1. Strings in Python are sequential collections of only characters. A character is a string of length 1. In Python, the for loop iterates once for each item in some sequence type (i.e, a list, tuple, string). What do you guess would be printed by the following program if the user enters “Mark”? name = raw_input(“Enter your name: “) for ch in name: print ch print 'done' 2. Strings are immutable, but the sequence operations work on strings. Operations on strings (or any sequence collection) include: Operation Operator Explanation Example myString = “Hello World” otherString = “cat” Access the element specified myString[1] Indexing [ <index> ] by the index myString[ 1:5 ] Slicing [ : ] Extract a part of the string myString + otherString Concatenation + Combine strings together Concatenate a repeated otherString * 3 Repetition * number of times Ask whether a substring is in ‘orl’ in myString Membership in a string How many items are in the len( myString ) Length len(string) string? Result of Example ‘e’ ‘ello’ ‘Hello Worldcat’ ‘catcatcat’ True 11 For the following strings, predict the results: cheer = ‘GO Panthers!!!’ rhyme = ‘The cow jumped over the moon.’ 01234567891111111111222222222 0123456789012345678 Expression cheer[4] Predicted Result Actual Result cheer[2:6] cheer[:4] cheer[1:4] + rhyme[-3:] cheer[:2] * 3 ‘jump’ in rhyme len(cheer) cheer[2:4]*4 Lecture 10 Page 1 Intro. to Computing Name:___________________ 3. String objects also have the following methods: (string module can be imported to provide more operations.) Method Usage Explanation center myString.center(w) Returns a string with myString centered in a field of size w ljust myString.ljust(w) Returns a string with myString left-justified in a field of size w rjust myString.rjust(w) Returns a string with myString right-justified in a field of size w upper myString.upper( ) Returns a string with myString in all upper-case characters lower myString.lower( ) Returns a string with myString in all lower-case characters strip myString.strip( ) Returns a string with leading and trailing whitespace (space, tab, new-line) chars. removed. An optional string parameter can be used to supply characters to strip instead of whitespace. count myString.count(sub) Returns number of occurrences of sub in myString (Optional parameters: myString.count(sub [, start [, end] ] ) endswith myString.endswith(sub) Returns True if myString ends with the substring sub; otherwise it returns False startswith myString.startswith(sub) Returns True if myString starts with the substring sub; otherwise it returns False isdigit myString.isdigit( ) Returns True if myString contains only digits; otherwise it returns False isalpha myString.isalpha( ) Returns True if myString contains only letters; otherwise it returns False split myString.split( ) Returns a list of substrings of myString splits at whitespace characters. An optional string parameter can supply characters to split on. find myString.find(sub) Returns the starting index of the first occurrence of sub. (Optional parameters: myString.find(sub [, start [, end] ] ) replace myString.replace(old,new) Returns a string with all occurrences of substring old replaced by substring new. An additional integer parameter can specify the number of replacements to perform, e.g.,myString.replace(old,new, 3) Assume the following strings: path = “/home/usr/fienup/” str = ‘mouse’ data = ‘Python rules!’ What would be the result of each of the following? a) path.find(‘om’) b) path.count(‘/’) c) path.split(‘/’) d) path.upper().rjust(25) e) data.endswith(‘i’) f) “totally “.join(data.split()) 4. Using the variable from the above question, what string methods would perform the following tasks: a) Obtain a list of words in the string. b) Obtain the string converted to all upper-case letters. c) Locate the position of the substring “rules”. d) Replace the exclamation point with a question mark. Lecture 10 Page 2