Python Readline

Readline¶ Be carefully when using readline. Do specify a timeout when opening the serial port otherwise it could block forever if no newline character is received. Also note that readlines only works with a timeout. Readlines depends on having a timeout and interprets that as EOF (end of file). It raises an exception if the port is not. Python Serial.readline - 30 examples found. These are the top rated real world Python examples of serial.Serial.readline extracted from open source projects. You can rate examples to help us improve the quality of examples. How To Read a Text File Line by Line Using While Statement in Python? Here is the way to read text file one line at a time using 'While' statement and python's readline function. Since we read one line at a time with readline, we can easily handle big files without worrying about memory problems.

1. Python Readlines Eof
2. Read File Line By Line Python
3. Python Readline From File
4. Python Read Lines From File
5. Python Readlines From File
6. Python Readline Loop
7. Python Readline Csv

The readline module defines a number of functions to facilitatecompletion and reading/writing of history files from the Python interpreter.This module can be used directly, or via the rlcompleter module, whichsupports completion of Python identifiers at the interactive prompt. Settingsmade using this module affect the behaviour of both the interpreter'sinteractive prompt and the prompts offered by the built-in input()function.

Note

The underlying Readline library API may be implemented bythe libedit library instead of GNU readline.On MacOS X the readline module detects which library is being usedat run time.

The configuration file for libedit is different from thatof GNU readline. If you programmatically load configuration stringsyou can check for the text 'libedit' in readline.__doc__to differentiate between GNU readline and libedit.

Readline keybindings may be configured via an initialization file, typically.inputrc in your home directory. See Readline Init Filein the GNU Readline manual for information about the format andallowable constructs of that file, and the capabilities of theReadline library in general.

6.7.1. Init file¶

The following functions relate to the init file and user configuration:

Execute the init line provided in the string argument. This callsrl_parse_and_bind() in the underlying library.

Execute a readline initialization file. The default filename is the last filenameused. This calls rl_read_init_file() in the underlying library.

6.7.2. Line buffer¶

The following functions operate on the line buffer:

Return the current contents of the line buffer (rl_line_bufferin the underlying library).

Insert text into the line buffer at the cursor position. This callsrl_insert_text() in the underlying library, but ignoresthe return value.

Change what's displayed on the screen to reflect the current contents of theline buffer. This calls rl_redisplay() in the underlying library.

6.7.3. History file¶

The following functions operate on a history file:

Load a readline history file, and append it to the history list.The default filename is ~/.history. This callsread_history() in the underlying library.

Save the history list to a readline history file, overwriting anyexisting file. The default filename is ~/.history. This callswrite_history() in the underlying library.

Append the last nelements items of history to a file. The default filename is~/.history. The file must already exist. This callsappend_history() in the underlying library. This functiononly exists if Python was compiled for a version of the librarythat supports it.

Python Readlines Eof

Set or return the desired number of lines to save in the history file.The write_history_file() function uses this value to truncatethe history file, by calling history_truncate_file() inthe underlying library. Negative values implyunlimited history file size.

6.7.4. History list¶

The following functions operate on a global history list:

Clear the current history. This calls clear_history() in theunderlying library. The Python function only exists if Python wascompiled for a version of the library that supports it.

Return the number of items currently in the history. (This is different fromget_history_length(), which returns the maximum number of lines that willbe written to a history file.)

Return the current contents of history item at index. The item indexis one-based. This calls history_get() in the underlying library.

Remove history item specified by its position from the history.The position is zero-based. This calls remove_history() inthe underlying library.

Replace history item specified by its position with line.The position is zero-based. This calls replace_history_entry()in the underlying library.

Append line to the history buffer, as if it was the last line typed.This calls add_history() in the underlying library.

Enable or disable automatic calls to add_history() when readinginput via readline. The enabled argument should be a Boolean valuethat when true, enables auto history, and that when false, disablesauto history.

CPython implementation detail: Auto history is enabled by default, and changes to this do not persistacross multiple sessions.

6.7.5. Startup hooks¶

Set or remove the function invoked by the rl_startup_hookcallback of the underlying library. If function is specified, it willbe used as the new hook function; if omitted or None, any functionalready installed is removed. The hook is called with noarguments just before readline prints the first prompt.

Set or remove the function invoked by the rl_pre_input_hookcallback of the underlying library. If function is specified, it willbe used as the new hook function; if omitted or None, anyfunction already installed is removed. The hook is calledwith no arguments after the first prompt has been printed and just beforereadline starts reading input characters. This function only existsif Python was compiled for a version of the library that supports it.

6.7.6. Completion¶

The following functions relate to implementing a custom word completionfunction. This is typically operated by the Tab key, and can suggest andautomatically complete a word being typed. By default, Readline is set upto be used by rlcompleter to complete Python identifiers forthe interactive interpreter. If the readline module is to be usedwith a custom completer, a different set of word delimiters should be set.

Set or remove the completer function. If function is specified, it will beused as the new completer function; if omitted or None, any completerfunction already installed is removed. The completer function is called asfunction(text,state), for state in 0, 1, 2, ..., until itreturns a non-string value. It should return the next possible completionstarting with text.

The installed completer function is invoked by the entry_func callbackpassed to rl_completion_matches() in the underlying library.The text string comes from the first parameter to therl_attempted_completion_function callback of theunderlying library.

Get the completer function, or None if no completer function has been set.

Get the type of completion being attempted. This returns therl_completion_type variable in the underlying library asan integer.

Read File Line By Line Python

Get the beginning or ending index of the completion scope.These indexes are the start and end arguments passed to therl_attempted_completion_function callback of theunderlying library.

Set or get the word delimiters for completion. These determine thestart of the word to be considered for completion (the completion scope).These functions access the rl_completer_word_break_charactersvariable in the underlying library.

Set or remove the completion display function. If function isspecified, it will be used as the new completion display function;if omitted or None, any completion display function alreadyinstalled is removed. This sets or clears therl_completion_display_matches_hook callback in theunderlying library. The completion display function is called asfunction(substitution,[matches],longest_match_length) onceeach time matches need to be displayed.

6.7.7. Example¶

The following example demonstrates how to use the readline module'shistory reading and writing functions to automatically load and save a historyfile named .python_history from the user's home directory. The codebelow would normally be executed automatically during interactive sessionsfrom the user's PYTHONSTARTUP file.

This code is actually automatically run when Python is run ininteractive mode (see Readline configuration).

The following example achieves the same goal but supports concurrent interactivesessions, by only appending the new history.

The following example extends the code.InteractiveConsole class tosupport history save/restore.

Contents

Read Text File in Python

To read text file in Python, follow these steps.

1. Call open() builtin function with filepath and mode passed as arguments. open() function returns a file object.
2. Call read() method on the file object. read() returns a string.
3. The returned string is the complete text from the text file.

Example 1: Read Text File

In the following Python program, we will open sample.txt file in read mode. We will read all the contents of the text file and print the text to the console.

Python Program

Output

You can provide the complete or absolute path to the open() function or provide a relative path if the base path is present in the PATH environment variable.

Example 2: Read only Some Characters in the Text File

If you need to read only specific number of characters, say N number of characters, present at the starting of the file, pass N (number) as argument to read() function.

In the following Python program, we will read first 20 characters in the file.

Python Program

Output

read(20) function returned the first 20 characters from the text file.

Example 3: Read file in Text mode

read, write and execute modes are based on the permissions. There are text and binary based on the nature of content.

In the following example, we will open the file in text mode explicitly by providing 't' along with the read 'r' mode.

Change what's displayed on the screen to reflect the current contents of theline buffer. This calls rl_redisplay() in the underlying library.

6.7.3. History file¶

The following functions operate on a history file:

Load a readline history file, and append it to the history list.The default filename is ~/.history. This callsread_history() in the underlying library.

Save the history list to a readline history file, overwriting anyexisting file. The default filename is ~/.history. This callswrite_history() in the underlying library.

Append the last nelements items of history to a file. The default filename is~/.history. The file must already exist. This callsappend_history() in the underlying library. This functiononly exists if Python was compiled for a version of the librarythat supports it.

Python Readlines Eof

Set or return the desired number of lines to save in the history file.The write_history_file() function uses this value to truncatethe history file, by calling history_truncate_file() inthe underlying library. Negative values implyunlimited history file size.

6.7.4. History list¶

The following functions operate on a global history list:

Clear the current history. This calls clear_history() in theunderlying library. The Python function only exists if Python wascompiled for a version of the library that supports it.

Return the number of items currently in the history. (This is different fromget_history_length(), which returns the maximum number of lines that willbe written to a history file.)

Return the current contents of history item at index. The item indexis one-based. This calls history_get() in the underlying library.

Remove history item specified by its position from the history.The position is zero-based. This calls remove_history() inthe underlying library.

Replace history item specified by its position with line.The position is zero-based. This calls replace_history_entry()in the underlying library.

Append line to the history buffer, as if it was the last line typed.This calls add_history() in the underlying library.

Enable or disable automatic calls to add_history() when readinginput via readline. The enabled argument should be a Boolean valuethat when true, enables auto history, and that when false, disablesauto history.

CPython implementation detail: Auto history is enabled by default, and changes to this do not persistacross multiple sessions.

6.7.5. Startup hooks¶

Set or remove the function invoked by the rl_startup_hookcallback of the underlying library. If function is specified, it willbe used as the new hook function; if omitted or None, any functionalready installed is removed. The hook is called with noarguments just before readline prints the first prompt.

Set or remove the function invoked by the rl_pre_input_hookcallback of the underlying library. If function is specified, it willbe used as the new hook function; if omitted or None, anyfunction already installed is removed. The hook is calledwith no arguments after the first prompt has been printed and just beforereadline starts reading input characters. This function only existsif Python was compiled for a version of the library that supports it.

6.7.6. Completion¶

The following functions relate to implementing a custom word completionfunction. This is typically operated by the Tab key, and can suggest andautomatically complete a word being typed. By default, Readline is set upto be used by rlcompleter to complete Python identifiers forthe interactive interpreter. If the readline module is to be usedwith a custom completer, a different set of word delimiters should be set.

Set or remove the completer function. If function is specified, it will beused as the new completer function; if omitted or None, any completerfunction already installed is removed. The completer function is called asfunction(text,state), for state in 0, 1, 2, ..., until itreturns a non-string value. It should return the next possible completionstarting with text.

The installed completer function is invoked by the entry_func callbackpassed to rl_completion_matches() in the underlying library.The text string comes from the first parameter to therl_attempted_completion_function callback of theunderlying library.

Get the completer function, or None if no completer function has been set.

Get the type of completion being attempted. This returns therl_completion_type variable in the underlying library asan integer.

Read File Line By Line Python

Get the beginning or ending index of the completion scope.These indexes are the start and end arguments passed to therl_attempted_completion_function callback of theunderlying library.

Set or get the word delimiters for completion. These determine thestart of the word to be considered for completion (the completion scope).These functions access the rl_completer_word_break_charactersvariable in the underlying library.

Set or remove the completion display function. If function isspecified, it will be used as the new completion display function;if omitted or None, any completion display function alreadyinstalled is removed. This sets or clears therl_completion_display_matches_hook callback in theunderlying library. The completion display function is called asfunction(substitution,[matches],longest_match_length) onceeach time matches need to be displayed.

6.7.7. Example¶

The following example demonstrates how to use the readline module'shistory reading and writing functions to automatically load and save a historyfile named .python_history from the user's home directory. The codebelow would normally be executed automatically during interactive sessionsfrom the user's PYTHONSTARTUP file.

This code is actually automatically run when Python is run ininteractive mode (see Readline configuration).

The following example achieves the same goal but supports concurrent interactivesessions, by only appending the new history.

The following example extends the code.InteractiveConsole class tosupport history save/restore.

Contents

Read Text File in Python

To read text file in Python, follow these steps.

1. Call open() builtin function with filepath and mode passed as arguments. open() function returns a file object.
2. Call read() method on the file object. read() returns a string.
3. The returned string is the complete text from the text file.

Example 1: Read Text File

In the following Python program, we will open sample.txt file in read mode. We will read all the contents of the text file and print the text to the console.

Python Program

Output

You can provide the complete or absolute path to the open() function or provide a relative path if the base path is present in the PATH environment variable.

Example 2: Read only Some Characters in the Text File

If you need to read only specific number of characters, say N number of characters, present at the starting of the file, pass N (number) as argument to read() function.

In the following Python program, we will read first 20 characters in the file.

Python Program

Output

read(20) function returned the first 20 characters from the text file.

Example 3: Read file in Text mode

read, write and execute modes are based on the permissions. There are text and binary based on the nature of content.

In the following example, we will open the file in text mode explicitly by providing 't' along with the read 'r' mode.

Python Program

Python Readline From File

Output

Example 4: Read Text File Line by Line

Python Read Lines From File

To read text line by line from a file, use File.readline() function. File.readline() returns the current line and updates its pointer to the next line. So, when you call readline() function for the next time, the next line is returned.

Remember that readline() returns the line along with the new line character at the end of the line, except for the last line. So, if you do not require the new line character, you may use strip() function. There is a catch here. If your line contains white space characters at the start and end, and if you use strip(), you will loose those white space characters in the line.

In this example, we shall read the text file line by line.

Python Readlines From File

Python Program

Python Readline Loop

Output

Python Readline Csv

Summary

In this tutorial of Python Examples, we learned how to read a text file in Python with the help of well detailed Python example programs.