Lecture # 29 Python III: Editing a Text File in Python

Create a Text File: Georgie Porgie pudding and.py, Kissed the girls and made them cry When the boys came out to play, Georgie Porgie ran away.

Create a “Search & Replace” Python Program that will: Open the text file

Create a “Search & Replace” Python Program that will: Open the text file Input replacement text (name) from the keyboard

Create a “Search & Replace” Python Program that will: Open the text file Input replacement text (name) from the keyboard Search the text file to find the name “Georgie”

Create a “Search & Replace” Python Program that will: Open the text file Input replacement text (name) from the keyboard Search the text file to find the name “Georgie” Swap that name in place of “Georgie”

Create a “Search & Replace” Python Program that will: Open the text file Input replacement text (name) from the keyboard Search the text file to find the name “Georgie” Swap that name in place of “Georgie” Create and open a new file

Create a “Search & Replace” Python Program that will: Open the text file Input replacement text (name) from the keyboard Search the text file to find the name “Georgie” Swap that name in place of “Georgie” Create and open a new file Output the edited string to the new file

Create a “Search & Replace” Python Program that will: Open the text file Input replacement text (name) from the keyboard Search the text file to find the name “Georgie” Swap that name in place of “Georgie” Create and open a new file Output the edited string to the new file Close the new file

Create a “Search & Replace” Python Program that will: Open the text file: f = open(pickAFile())

Create a “Search & Replace” Python Program that will: Input replacement text (name) from the keyboard:

Create a “Search & Replace” Python Program that will: Input replacement text (name) from the keyboard: r = raw_input("Input replacement name: ”)

Create a “Search & Replace” Python Program that will: Search the text file to find the name “Georgie”: s = f.read() reads text file containing “Georgie” into string, s s.find(“Georgie”) finds “Georgie” in string, s returns index of the “G”. Georgie Porgie pudding and index …

Create a “Search & Replace” Python Program that will: In this case index = 0, for first occurrence of “Georgie.” Georgie Porgie pudding and index … In general, s.find returns index of first occurrence of substring that is found.

Create a “Search & Replace” Python Program that will: Swap that name in place of “Georgie”: let r = “Jimmy” p = “Georgie”

Create a “Search & Replace” Python Program that will: Swap that name in place of “Georgie”: let r = “Jimmy” p = “Georgie” t = r + s[s.find("Georgie",0,len(s))+len(p):len(s)] find Georgie between index 0 and len(s) skip past Georgie

Create a “Search & Replace” Python Program that will: Swap that name in place of “Georgie”: let r = “Jimmy” p = “Georgie” t = r + s[s.find("Georgie",0,len(s))+len(p):len(s)] t = Jimmy + _Porgie pudding and.py, … Georgie Porgie pudding and.py, find Georgie between index 0 and len(s) skip past Georgie

Create a “Search & Replace” Python Program that will: Since there are actually 2 occurrences of “Georgie”: Do t = r + s[s.find("Georgie",0,len(s))+len(p): s.find("Georgie",len(p),len(s))] s[n:m] references the portion of string s that we want to concatenate to r. find Georgie between index 0 and len(s)

Create a “Search & Replace” Python Program that will: Since there are actually 2 occurrences of “Georgie”: Do t = r + s[s.find("Georgie",0,len(s))+len(p): s.find("Georgie",len(p),len(s))] + r + s[s.find("Georgie",len(p),len(s)) + len(p):len(s)] get the second occurrence of Georgie find Georgie between index 0 and len(s)

Create a “Search & Replace” Python Program that will: Create and open a new (edied) file: g = open(“… put in file path here …” + r (Call file new name, Jimmy) + “.txt”,”wt”) - text extension - open for writing Borrow from f

Create a “Search & Replace” Python Program that will: Output the edited string, t, to the new file: g.write(t) g.close() And be sure to close the file

Algorithms for Basic Word Processing  Type a character Delete a character Select some characters Bold some characters Cut / Copy / Paste

Cursor Position: an index into the string Cursor = 3 Cursor=6

Typing a Character Cursor=4 Cursor = 3 Key = ‘ p ’

Typing a Character Cursor = 3 Key = ‘ p ’ For ( index I starting at Text.length-1 down to Cursor) {Text[I+1]=Text[I] } Text[Cursor] = Key; Cursor = Cursor+1;

Typing a Character Cursor = 3 Key = ‘ p ’ I=8 For ( index I starting at Text.length-1 down to Cursor) {Text[I+1]=Text[I] } move character up one space Text[Cursor] = Key; Cursor = Cursor+1;

Typing a Character Cursor = 3 Key = ‘ p ’ I=7 For ( index I starting at Text.length-1 down to Cursor) {Text[I+1]=Text[I] } move character up one space Text[Cursor] = Key; Cursor = Cursor+1;

Typing a Character Cursor = 3 Key = ‘ p ’ I=6 For ( index I starting at Text.length-1 down to Cursor) {Text[I+1]=Text[I] } move character up one space Text[Cursor] = Key; Cursor = Cursor+1;

Typing a Character Cursor = 3 Key = ‘ p ’ I=5 For ( index I starting at Text.length-1 down to Cursor) {Text[I+1]=Text[I] } move character up one space Text[Cursor] = Key; Cursor = Cursor+1;

Typing a Character Cursor = 3 Key = ‘ p ’ I=4 For ( index I starting at Text.length-1 down to Cursor) {Text[I+1]=Text[I] } move character up one space Text[Cursor] = Key; Cursor = Cursor+1;

Typing a Character Cursor = 3 Key = ‘ p ’ I=3 For ( index I starting at Text.length-1 down to Cursor) {Text[I+1]=Text[I] } Text[Cursor] = Key; add the typed character Cursor = Cursor+1;

Typing a Character Cursor = 4 Key = ‘ p ’ I=3 For ( index I starting at Text.length-1 down to Cursor) {Text[I+1]=Text[I] } Text[Cursor] = Key; Cursor = Cursor+1; move the cursor over

Algorithms for Basic Word Processing Type a character  Delete a character Select some characters Bold some characters Cut / Copy / Paste

Delete a Character Cursor = 4 Key = delete I=? For ( index I starting at Cursor+1 up to Text.length-1) {Text[I-1]=Text[I] } move a character down one space Cursor = Cursor-1; Text[Text.length-1] = “ no character ”

Delete a Character Cursor = 4 Key = delete I=3 For ( index I starting at Cursor+1 up to Text.length-1) {Text[I-1]=Text[I] } move a character down one space Cursor = Cursor-1; Text[Text.length-1] = “ no character ”

Delete a Character Cursor = 4 Key = delete I=4 For ( index I starting at Cursor+1 up to Text.length-1) {Text[I-1]=Text[I] } move a character down one space Cursor = Cursor-1; Text[Text.length-1] = “ no character ”

Delete a Character Cursor = 4 Key = delete I=5 For ( index I starting at Cursor+1 up to Text.length-1) {Text[I-1]=Text[I] } move a character down one space Cursor = Cursor-1; Text[Text.length-1] = “ no character ”

Delete a Character Cursor = 4 Key = delete I=6 For ( index I starting at Cursor+1 up to Text.length-1) {Text[I-1]=Text[I] } move a character down one space Cursor = Cursor-1; Text[Text.length-1] = “ no character ”

Delete a Character Cursor = 4 Key = delete I=7 For ( index I starting at Cursor+1 up to Text.length-1) {Text[I-1]=Text[I] } move a character down one space Cursor = Cursor-1; Text[Text.length-1] = “ no character ”

Delete a Character Cursor = 3 Key = delete I=8 For ( index I starting at Cursor+1 up to Text.length-1) {Text[I-1]=Text[I] } Cursor = Cursor-1;move the cursor over Text[Text.length-1] = “ no character ”

Delete a Character Cursor = 3 Key = delete I=8 For ( index I starting at Cursor+1 up to Text.length-1) {Text[I-1]=Text[I] } Cursor = Cursor-1; Text[Text.length-1] = “ no character ” ; blank out last character

A Helpful Function Function moveChars(Text,Start,End,Distance) {if (Distance>0) {for (index I from End down to Start ) { Text[I+Distance]=Text[I];} } Else {for (index I from Start up to End ) { Text[I+Distance]=Text[I] } }

Typing a Character Cursor = 3 Key = ‘ p ’ moveChars(text,Cursor,text.length-1, 1); Text[Cursor]=Key; Cursor=Cursor+1;

Delete a Character Cursor = 4 Key = delete I=? moveChars(text,cursor,text.length-1,-1); Cursor=Cursor-1; text[text.length -1]=no character;

Algorithms for Basic Word Processing Type a character Delete a character  Select some characters Bold some characters Cut / Copy / Paste

Selecting Characters Start = 2 End = 7

Algorithms for Basic Word Processing Type a character Delete a character Select some characters  Bold some characters Cut / Copy / Paste

Bolding Characters Start = 2 End = 7 moveChars(text,End,text.length-1,2); moveChars(text,Start,End-1,1); Text[Start]=code for start bold; Text[End+1]=code for end bold; End=End+2;

Bolding Characters Start = 2 End = 7 moveChars(text,End,text.length-1,2); -> moveChars(text,7,7,2) moveChars(text,Start,End-1,1); Text[Start]=code for start bold; Text[End+1]=code for end bold; End=End+2;

Bolding Characters Start = 2 End = 7 moveChars(text,End,text.length-1,2); moveChars(text,Start,End-1,1); -> moveChars(text,2,6,1) Text[Start]=code for start bold; Text[End+1]=code for end bold; End=End+2;

Bolding Characters Start = 2 End = 7 moveChars(text,End,text.length-1,2); moveChars(text,Start,End-1,1); Text[Start]=code for start bold; Text[End+1]=code for end bold; End=End+2;

Bolding Characters Start = 2 End = 7 moveChars(text,End,text.length-1,2); moveChars(text,Start,End-1,1); Text[Start]=code for start bold; Text[End+1]=code for end bold; End=End+2;

Bolding Characters Start = 2 End = 9 moveChars(text,End,text.length-1,2); moveChars(text,Start,End-1,1); Text[Start]=code for start bold; Text[End+1]=code for end bold; End=End+2;

Algorithms for Basic Word Processing Type a character Delete a character Select some characters Bold some characters  Cut / Copy / Paste

Cut Start = 2 End = 7 ClipBoard= For (each character C with index >= Start and < End) { copy C to the ClipBoard } moveChars(text,End,text.length-1,Start-End); Set the last (End-Start) characters in the array to “ no character ” End=Start;

Cut Start = 2 End = 7 ClipBoard= “ strin ” For (each character C with index >= Start and < End) { copy C to the ClipBoard } moveChars(text,End,text.length-1,Start-End); Set the last (End-Start) characters in the array to “ no character ” End=Start;

Cut Start = 2 End = 7 ClipBoard = “ strin ” For (each character C with index >= Start and < End) { copy C to the ClipBoard } moveChars(text,End,text.length-1,Start-End); Set the last (End-Start) characters in the array to “ no character ” End=Start;

Cut Start = 2 End = 7 ClipBoard = “ strin ” For (each character C with index >= Start and < End) { copy C to the ClipBoard } moveChars(text,End,text.length-1,Start-End); Set the last (End-Start) characters in the array to “ no character ” End=Start;

Cut Start = 2 End = 2 ClipBoard = “ strin ” For (each character C with index >= Start and < End) { copy C to the ClipBoard } moveChars(text,End,text.length-1,Start-End); Set the last (End-Start) characters in the array to “ no character ” End=Start;

Copy Start = 2 End = 7 ClipBoard = “ strin ” For (each character C with index >= Start and < End) { copy C to the ClipBoard }

Paste Start = 2 End = 2 ClipBoard = “ strin ” moveChars(text,End,text.length-1, ClipBoard.length); Copy the characters from ClipBoard into the array at index Start

Paste Start = 2 End = 2 ClipBoard = “ strin ” moveChars(text,End,text.length-1, ClipBoard.length); Copy the characters from ClipBoard into the array at index Start

Paste Start = 2 End = 2 ClipBoard = “ strin ” moveChars(text,End,text.length-1, ClipBoard.length); Copy the characters from ClipBoard into the array at index Start

More about Python

String Encodings ASCII –special characters: \n = Linefeed \r = Carriage return \t = Horizontal Tab Unicode –u”…..”

Accessing Substrings str[i] – getting the i th character in str len(str) – returns the length of the str slices –str[n:m] – str[n] through str[m-1] –str[:m] – str[0] through str[m-1] –str[n:] – str[n] through str[len(str)-1] –str[:] – str[0] through str[len(str)-1] The entire string –str[-1:] – str[len(str)-1] through str[len(str)-1] A sequence with 1 character, the last character –str[:-1] – str[0] through str[len(str)-2] Demo

String Methods String methods –capitalize() – only the first word in the string –startswith(prefix) – returns 1 or 0 –endswith(suffix) –find(str), find(str, start), find(str, start, end) returns -1 if string not found –rfind variant –upper(), lower(), swapcase() String methods –isalpha() –isdigit() –replace(string, replacement)

Importing Modules Decomposing a program into parts or modules Module is a python file –Ends in “.py” Python file contains methods, variables, and classes Forms of import –import file_name Assumes file_name ends in “.py” Must use full path name to access member of module –from file_name import * –from file_name import x, y, z –import x as y

Examples Form Letter – Program_91.py (and command line)Program_91.py changeLittle Example – Program_92.py (and command line)Program_92.py –use sample.py as first parameter findSequence – Program_93.py (and command line)Program_93.py replaceAllOccurrences – Program_94.pyProgram_94.py –use sample.py again Web Scraping – Program_95.pyProgram_95.py titleDirectory – Program_96.pyProgram_96.py –setMediaPath to MediaSources random – Program_97.pyProgram_97.py random sentences –Execution of a module from command line Program_97a.py Program_97b.py –Including a main routine import97a.py import97b.py

Built in Python Modules (The Python library) Often used modules –os, sys, random –datetime, calendar –calendar –math –zipfile – –SimpleHTTPServer Why use modules –Save work, why reinvent the wheel? –Higher quality Fewer bugs Run faster Well documented

Lists Literals –a = [1, 2, 3, 4] Access –a[i] for loops –for i in a: Concatenation –“+” operator Lists of lists –access – a[i][j] Methods –append(element) –remove(something) –sort() –reverse() –count() –split(delimeter) strings to lists of strings Functions –max(list) –min(list)

Files List of bytes Name Suffix –Type of information in file Folder or Directory Structure –Trees Trees as lists of lists of lists of … –Traversing a tree with dot notation From root –Traversing domain names students.cs.byu.edu