Python write to file special characters
Escape CharactersTo insert characters that are illegal in a string, use an escape character. Show
An escape character is a backslash An example of an illegal character is a double quote inside a string that is surrounded by double quotes: ExampleYou will get an error if you use double quotes inside a string that is surrounded by double quotes: txt = "We are the so-called "Vikings" from the north." Try it Yourself » To fix this problem, use the escape character ExampleThe escape character allows you to use double quotes when you normally would not be allowed: txt = "We are the so-called \"Vikings\" from the north." Try it Yourself » Other escape characters used in Python:
I'm using Python to process some plain text into LaTeX, so I need to be able to write things like How do I get Python to write The code is something like this ... Python 3, Mac OS 10.5 PPC One solution is to escape the escape character ( This will be written to the file as (I assume that the You just need to double the backslash: You can also use raw strings: Note the 'r' before \begin 1.12 This HOWTO discusses Python’s support for the Unicode specification for representing textual data, and explains various problems that people commonly encounter when trying to work with Unicode. Introduction to Unicode¶Definitions¶Today’s programs need to be able to handle a wide variety of characters. Applications are often internationalized to display messages and output in a variety of user-selectable languages; the same program might need to output an error message in English, French, Japanese, Hebrew, or Russian. Web content can be written in any of these languages and can also include a variety of emoji symbols. Python’s string type uses the Unicode Standard for representing characters, which lets Python programs work with all these different possible characters. Unicode (https://www.unicode.org/) is a specification that aims to list every character used by human languages and give each character its own unique code. The Unicode specifications are continually revised and updated to add new languages and symbols. A character is the smallest possible component of a text. ‘A’, ‘B’, ‘C’, etc., are all different characters. So are ‘È’ and ‘Í’. Characters vary depending on the language or context you’re talking about. For example, there’s a character for “Roman Numeral One”, ‘Ⅰ’, that’s separate from the uppercase letter ‘I’. They’ll usually look the same, but these are two different characters that have different meanings. The Unicode standard describes how characters are represented by code points. A code point value is an integer in the range 0 to 0x10FFFF (about 1.1 million values, the actual number assigned is less than that). In the standard and in this document, a code point is
written using the notation The Unicode standard contains a lot of tables listing characters and their corresponding code points: 0061 'a'; LATIN SMALL LETTER A 0062 'b'; LATIN SMALL LETTER B 0063 'c'; LATIN SMALL LETTER C ... 007B '{'; LEFT CURLY BRACKET ... 2167 'Ⅷ'; ROMAN NUMERAL EIGHT 2168 'Ⅸ'; ROMAN NUMERAL NINE ... 265E '♞'; BLACK CHESS KNIGHT 265F '♟'; BLACK CHESS PAWN ... 1F600 '😀'; GRINNING FACE 1F609 '😉'; WINKING FACE ... Strictly, these definitions imply that it’s meaningless to say ‘this is character A character is represented on a screen or on paper by a set of graphical elements that’s called a glyph. The glyph for an uppercase A, for example, is two diagonal strokes and a horizontal stroke, though the exact details will depend on the font being used. Most Python code doesn’t need to worry about glyphs; figuring out the correct glyph to display is generally the job of a GUI toolkit or a terminal’s font renderer. Encodings¶To summarize the previous section: a Unicode string is a sequence of code points, which are numbers from 0 through The first encoding you might think of is using 32-bit integers as the code unit, and then using the CPU’s representation of 32-bit integers. In this representation, the string “Python” might look like this: P y t h o n 0x50 00 00 00 79 00 00 00 74 00 00 00 68 00 00 00 6f 00 00 00 6e 00 00 00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 This representation is straightforward but using it presents a number of problems.
Therefore this encoding isn’t used very much, and people instead choose other encodings that are more efficient and convenient, such as UTF-8. UTF-8 is one of the most commonly used encodings, and Python often defaults to using it. UTF stands for “Unicode Transformation Format”, and the ‘8’ means that 8-bit values are used in the encoding. (There are also UTF-16 and UTF-32 encodings, but they are less frequently used than UTF-8.) UTF-8 uses the following rules:
UTF-8 has several convenient properties:
References¶The Unicode Consortium site has character charts, a glossary, and PDF versions of the Unicode specification. Be prepared for some difficult reading. A chronology of the origin and development of Unicode is also available on the site. On the Computerphile Youtube channel, Tom Scott briefly discusses the history of Unicode and UTF-8 (9 minutes 36 seconds). To help understand the standard, Jukka Korpela has written an introductory guide to reading the Unicode character tables. Another good introductory article was written by Joel Spolsky. If this introduction didn’t make things clear to you, you should try reading this alternate article before continuing. Wikipedia entries are often helpful; see the entries for “character encoding” and UTF-8, for example. Python’s Unicode Support¶Now that you’ve learned the rudiments of Unicode, we can look at Python’s Unicode features. The String Type¶Since Python 3.0, the language’s The default encoding for Python source code is UTF-8, so you can simply include a Unicode character in a string literal: try: with open('/tmp/input.txt', 'r') as f: ... except OSError: # 'File not found' error message. print("Fichier non trouvé") Side note: Python 3 also supports using Unicode characters in identifiers: répertoire = "/tmp/records.log" with open(répertoire, "w") as f: f.write("test\n") If you can’t enter a particular character in your editor or want to keep the source code ASCII-only for some reason, you can also use escape sequences in string literals. (Depending on your system, you may see the actual capital-delta glyph instead of a u escape.) >>> "\N{GREEK CAPITAL LETTER DELTA}" # Using the character name '\u0394' >>> "\u0394" # Using a 16-bit hex value '\u0394' >>> "\U00000394" # Using a 32-bit hex value '\u0394' In addition, one can create a string using the The errors argument specifies the response when the input string can’t be converted according to the encoding’s rules. Legal values for this argument are >>> b'\x80abc'.decode("utf-8", "strict") Traceback (most recent call last): ... UnicodeDecodeError: 'utf-8' codec can't decode byte 0x80 in position 0: invalid start byte >>> b'\x80abc'.decode("utf-8", "replace") '\ufffdabc' >>> b'\x80abc'.decode("utf-8", "backslashreplace") '\\x80abc' >>> b'\x80abc'.decode("utf-8", "ignore") 'abc' Encodings are specified as strings containing the encoding’s name. Python comes with roughly 100 different encodings; see the Python Library Reference at Standard Encodings for a list. Some encodings have multiple names; for example, One-character
Unicode strings can also be created with the >>> chr(57344) '\ue000' >>> ord('\ue000') 57344 Converting to Bytes¶The opposite method of The errors parameter is the same as the parameter of the The following example shows the different results: >>> u = chr(40960) + 'abcd' + chr(1972) >>> u.encode('utf-8') b'\xea\x80\x80abcd\xde\xb4' >>> u.encode('ascii') Traceback (most recent call last): ... UnicodeEncodeError: 'ascii' codec can't encode character '\ua000' in position 0: ordinal not in range(128) >>> u.encode('ascii', 'ignore') b'abcd' >>> u.encode('ascii', 'replace') b'?abcd?' >>> u.encode('ascii', 'xmlcharrefreplace') b'ꀀabcd' >>> u.encode('ascii', 'backslashreplace') b'\\ua000abcd\\u07b4' >>> u.encode('ascii', 'namereplace') b'\\N{YI SYLLABLE IT}abcd\\u07b4' The low-level routines for registering and accessing the available encodings are found in the
Unicode Literals in Python Source Code¶In Python source code, specific Unicode code points can be written using the >>> s = "a\xac\u1234\u20ac\U00008000" ... # ^^^^ two-digit hex escape ... # ^^^^^^ four-digit Unicode escape ... # ^^^^^^^^^^ eight-digit Unicode escape >>> [ord(c) for c in s] [97, 172, 4660, 8364, 32768] Using escape sequences for code points greater than 127 is fine in small doses, but becomes an annoyance if you’re using many accented characters, as you would in a program with messages in French or some other accent-using language. You can also assemble strings using the
Ideally, you’d want to be able to write literals in your language’s natural encoding. You could then edit Python source code with your favorite editor which would display the accented characters naturally, and have the right characters used at runtime. Python supports writing source code in UTF-8 by default, but you can use almost any encoding if you declare the encoding being used. This is done by including a special comment as either the first or second line of the source file: #!/usr/bin/env python # -*- coding: latin-1 -*- u = 'abcdé' print(ord(u[-1])) The syntax is inspired by Emacs’s notation for specifying variables local to a file. Emacs supports many different variables, but Python only supports ‘coding’. The If you don’t include such a comment, the default encoding used will be UTF-8 as already mentioned. See also PEP 263 for more information. Unicode Properties¶The Unicode specification includes a database of information about code points. For each defined code point, the information includes the character’s name, its category, the numeric value if applicable (for characters representing numeric concepts such as the Roman numerals, fractions such as one-third and four-fifths, etc.). There are also display-related properties, such as how to use the code point in bidirectional text. The following program displays some information about several characters, and prints the numeric value of one particular character: import unicodedata u = chr(233) + chr(0x0bf2) + chr(3972) + chr(6000) + chr(13231) for i, c in enumerate(u): print(i, '%04x' % ord(c), unicodedata.category(c), end=" ") print(unicodedata.name(c)) # Get numeric value of second character print(unicodedata.numeric(u[1])) When run, this prints: 0 00e9 Ll LATIN SMALL LETTER E WITH ACUTE 1 0bf2 No TAMIL NUMBER ONE THOUSAND 2 0f84 Mn TIBETAN MARK HALANTA 3 1770 Lo TAGBANWA LETTER SA 4 33af So SQUARE RAD OVER S SQUARED 1000.0 The category codes are abbreviations describing the nature of the character. These are grouped into categories such as “Letter”, “Number”, “Punctuation”, or “Symbol”, which in turn are broken up into subcategories. To take the codes from the above output, Comparing Strings¶Unicode adds some complication to comparing strings, because the same set of characters can be represented by different sequences of code points. For example, a letter like ‘ê’ can be represented as a single code point U+00EA, or as U+0065 U+0302, which is the code point for ‘e’ followed by a code point for ‘COMBINING CIRCUMFLEX ACCENT’. These will produce the same output when printed, but one is a string of length 1 and the other is of length 2. One tool for a case-insensitive comparison is the
>>> street = 'Gürzenichstraße' >>> street.casefold() 'gürzenichstrasse' A second tool is the
import unicodedata def compare_strs(s1, s2): def NFD(s): return unicodedata.normalize('NFD', s) return NFD(s1) == NFD(s2) single_char = 'ê' multiple_chars = '\N{LATIN SMALL LETTER E}\N{COMBINING CIRCUMFLEX ACCENT}' print('length of first string=', len(single_char)) print('length of second string=', len(multiple_chars)) print(compare_strs(single_char, multiple_chars)) When run, this outputs: $ python3 compare-strs.py length of first string= 1 length of second string= 2 True The first argument to the The Unicode Standard also specifies how to do caseless comparisons: import unicodedata def compare_caseless(s1, s2): def NFD(s): return unicodedata.normalize('NFD', s) return NFD(NFD(s1).casefold()) == NFD(NFD(s2).casefold()) # Example usage single_char = 'ê' multiple_chars = '\N{LATIN CAPITAL LETTER E}\N{COMBINING CIRCUMFLEX ACCENT}' print(compare_caseless(single_char, multiple_chars)) This will print Unicode Regular Expressions¶The regular expressions supported by the The string in this example has the number 57 written in both Thai and Arabic numerals: import re p = re.compile(r'\d+') s = "Over \u0e55\u0e57 57 flavours" m = p.search(s) print(repr(m.group())) When executed, Similarly, References¶Some good alternative discussions of Python’s Unicode support are:
The The documentation for the The documentation for the Marc-André Lemburg gave a presentation titled “Python and Unicode” (PDF slides) at EuroPython 2002. The slides are an excellent overview of the design of Python 2’s
Unicode features (where the Unicode string type is called Reading and Writing Unicode Data¶Once you’ve written some code that works with Unicode data, the next problem is input/output. How do you get Unicode strings into your program, and how do you convert Unicode into a form suitable for storage or transmission? It’s possible that you may not need to do anything depending on your input sources and output destinations; you should check whether the libraries used in your application support Unicode natively. XML parsers often return Unicode data, for example. Many relational databases also support Unicode-valued columns and can return Unicode values from an SQL query. Unicode data is usually converted to
a particular encoding before it gets written to disk or sent over a socket. It’s possible to do all the work yourself: open a file, read an 8-bit bytes object from it, and convert the bytes with One problem is the multi-byte nature of encodings; one Unicode character can be represented by several bytes. If you want to read the file in arbitrary-sized chunks (say, 1024 or 4096 bytes), you need to write error-handling code to catch the case where only part of the bytes encoding a single Unicode character are read at the end of a chunk. One solution would be to read the entire file into memory and then perform the decoding, but that prevents you from working with files that are extremely large; if you need to read a 2 GiB file, you need 2 GiB of RAM. (More, really, since for at least a moment you’d need to have both the encoded string and its Unicode version in memory.) The solution would be to use the low-level
decoding interface to catch the case of partial coding sequences. The work of implementing this has already been done for you: the built-in Reading Unicode from a file is therefore simple: with open('unicode.txt', encoding='utf-8') as f: for line in f: print(repr(line)) It’s also possible to open files in update mode, allowing both reading and writing: with open('test', encoding='utf-8', mode='w+') as f: f.write('\u4500 blah blah blah\n') f.seek(0) print(repr(f.readline()[:1])) The Unicode character In some areas, it is also convention to use a “BOM” at the start of UTF-8 encoded files; the name is misleading since UTF-8 is not byte-order dependent. The mark simply announces that the file is encoded in UTF-8. For reading such files, use the ‘utf-8-sig’ codec to automatically skip the mark if present. Unicode filenames¶Most of the operating systems in common use today support filenames that contain arbitrary Unicode characters. Usually this is implemented by converting the Unicode string into some encoding that varies depending on the system. Today Python is converging on using UTF-8: Python on MacOS has used UTF-8 for several versions, and Python 3.6 switched to
using UTF-8 on Windows as well. On Unix systems, there will only be a filesystem encoding. if you’ve set the The filename = 'filename\u4500abc' with open(filename, 'w') as f: f.write('blah\n') Functions in the The fn = 'filename\u4500abc' f = open(fn, 'w') f.close() import os print(os.listdir(b'.')) print(os.listdir('.')) will produce the following output: $ python listdir-test.py [b'filename\xe4\x94\x80abc', ...] ['filename\u4500abc', ...] The first list contains UTF-8-encoded filenames, and the second list contains the Unicode versions. Note that on most occasions, you should can just stick with using Unicode with these APIs. The bytes APIs should only be used on systems where undecodable file names can be present; that’s pretty much only Unix systems now. Tips for Writing Unicode-aware Programs¶This section provides some suggestions on writing software that deals with Unicode. The most important tip is:
If you attempt to write processing functions that accept both Unicode and byte strings, you will find your program vulnerable to bugs wherever you combine the two different kinds of strings. There is no automatic encoding or decoding: if you do e.g. When using data coming from a web browser or some other untrusted source, a common technique is to check for illegal characters in a string before using the string in a generated command line or storing it in a database. If you’re doing this, be careful to check the decoded string, not the encoded bytes data; some encodings may have interesting properties, such as not being bijective or not being fully ASCII-compatible. This is especially true if the input data also specifies the encoding, since the attacker can then choose a clever way to hide malicious text in the encoded bytestream. Converting Between File Encodings¶The
For example, if you have an input file f that’s in Latin-1, you can wrap it with a
new_f = codecs.StreamRecoder(f, # en/decoder: used by read() to encode its results and # by write() to decode its input. codecs.getencoder('utf-8'), codecs.getdecoder('utf-8'), # reader/writer: used to read and write to the stream. codecs.getreader('latin-1'), codecs.getwriter('latin-1') ) Files in an Unknown Encoding¶What can you do if you need to make a change to a file, but don’t know the
file’s encoding? If you know the encoding is ASCII-compatible and only want to examine or modify the ASCII parts, you can open the file with the with open(fname, 'r', encoding="ascii", errors="surrogateescape") as f: data = f.read() # make changes to the string 'data' with open(fname + '.new', 'w', encoding="ascii", errors="surrogateescape") as f: f.write(data) The References¶One section of Mastering Python 3 Input/Output, a PyCon 2010 talk by David Beazley, discusses text processing and binary data handling. The PDF slides for Marc-André Lemburg’s presentation “Writing Unicode-aware Applications in Python” discuss questions of character encodings as well as how to internationalize and localize an application. These slides cover Python 2.x only. The Guts of Unicode in Python is a PyCon 2013 talk by Benjamin Peterson that discusses the internal Unicode representation in Python 3.3. Acknowledgements¶The initial draft of this document was written by Andrew Kuchling. It has since been revised further by Alexander Belopolsky, Georg Brandl, Andrew Kuchling, and Ezio Melotti. Thanks to the following people who have noted errors or offered suggestions on this article: Éric Araujo, Nicholas Bastin, Nick Coghlan, Marius Gedminas, Kent Johnson, Ken Krugler, Marc-André Lemburg, Martin von Löwis, Terry J. Reedy, Serhiy Storchaka, Eryk Sun, Chad Whitacre, Graham Wideman. How do you escape special characters in Python?Escape sequences allow you to include special characters in strings. To do this, simply add a backslash ( \ ) before the character you want to escape.
How do you print special characters in Python?Use repr() to print special characters
Escaping special characters treats them as regular characters instead of commands for how to print the line. Call repr(string) to return string with special characters escaped.
How do you write a character in Python?Like many other popular programming languages, strings in Python are arrays of bytes representing unicode characters. However, Python does not have a character data type, a single character is simply a string with a length of 1. Square brackets can be used to access elements of the string.
How do you escape characters?Escape Characters
Use the backslash character to escape a single character or symbol. Only the character immediately following the backslash is escaped.
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