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encoding with open parameter vs encode string method byte size

I have come across something that I can't get my head around.
So I try to encode my string with one unicode character using both string encode method and open encoding parameter. For some reason, there is a difference regarding written byte size between these two methods.
Here is sample code:
with open("in.txt", "wb") as f:
no = f.write("Wlazł".encode("utf-8"))
print(no) # -> 6
with open("in.txt", "w", encoding="utf-8") as f:
no = f.write("Wlazł")
print(no) # -> 5
Does anyone know why this is so?

When you open a file in binary mode you get an instance of io.RawIOBase, and RawIOBase.write returns the number of bytes written.
When you open a file in text mode you get an instance of io.TextIOBase, and TextIOBase.write returns the number of characters written.
So the reason for the difference is that one is a count of bytes, the other of characters.

Writing more data to file than reading?

I am currently experimenting with how Python 3 handles bytes when reading, and writing data and I have come across a particularly troubling problem that I can't seem to find the source of. I am basically reading bytes out of a JPEG file, converting them to an integer using ord(), then returning the bytes to their original character using the line chr(character).encode('utf-8') and writing it back into a JPEG file. No issue right? Well when I go to try opening the JPEG file, I get a Windows 8.1 notification saying it can not open the photo. When I check the two files against each other one is 5.04MB, and the other is 7.63MB which has me awfully confused.
def __main__():
operating_file = open('photo.jpg', 'rb')
while True:
data_chunk = operating_file.read(64*1024)
if len(data_chunk) == 0:
print('COMPLETE')
break
else:
new_operation = open('newFile.txt', 'ab')
for character in list(data_chunk):
new_operation.write(chr(character).encode('utf-8'))
if __name__ == '__main__':
__main__()
This is the exact code I am using, any ideas on what is happening and how I can fix it?
NOTE: I am assuming that the list of numbers that list(data_chunk) provides is the equivalent to ord().

Here is a simple example you might wish to play with:
import sys
f = open('gash.txt', 'rb')
stuff=f.read() # stuff refers to a bytes object
f.close()
print(stuff)
f2 = open('gash2.txt', 'wb')
for i in stuff:
f2.write(i.to_bytes(1, sys.byteorder))
f2.close()
As you can see, the bytes object is iterable, but in the for loop we get back an int in i. To convert that to a byte I use int.to_bytes() method.

When you have a code point and you encode it in UTF-8, it is possible for the result to contain more bytes than the original.
For a specific example, refer to the WikiPedia page and consider the hexadecimal value 0xA2.
This is a single binary value, less than 255, but when encoded to UTF8 it becomes 0xC2, 0xA2.
Given that you are pulling bytes out of your source file, my first recommendation would be to simply pass the bytes directly to the writer of your target file.
If you are trying to understand how file I/O works, be wary of encode() when using a binary file mode. Binary files don't need to be encoded and or decoded - they are raw data.

Reading binary and text from same file in Python

How does one read binary and text from the same file in Python? I know how to do each separately, and can imagine doing both very carefully, but not both with the built-in IO library directly.
So I have a file that has a format that has large chunks of UTF-8 text interspersed with binary data. The text does not have a length written before it or a special character like "\0" delineating it from the binary data, there is a large portion of text near the end when parsed means "we are coming to an end".
The optimal solution would be to have the built-in file reading classes have "read(n)" and "read_char(n)" methods, but alas they don't. I can't even open the file twice, once as text and once as binary, since the return value of tell() on the text one can't be used with the binary one in any meaningful way.
So my first idea would be to open the whole file as binary and when I reach a chunk of text, read it "character by character" until I realize that the text is ending and then go back to reading it as binary. However this means that I have to read byte-by-byte and do my own decoding of UTF-8 characters (do I need to read another byte for this character before doing something with it?). If it was a fixed-width character encoding I would just read that many bytes each time. In the end I would also like the universal line endings as supported by the Python text-readers, but that would be even more difficult to implement while reading byte-by-byte.
Another easier solution would be if I could ask the text file object its real offset in the file. That alone would solve all my problems.

One way might be to use Hachoir to define a file parsing protocol.
The simple alternative is to open the file in binary mode and manually initialise a buffer and text wrapper around it. You can then switch in and out of binary pretty neatly:
my_file = io.open("myfile.txt", "rb")
my_file_buffer = io.BufferedReader(my_file, buffer_size=1) # Not as performant but a larger buffer will "eat" into the binary data
my_file_text_reader = io.TextIOWrapper(my_file_buffer, encoding="utf-8")
string_buffer = ""
while True:
while "near the end" not in string_buffer:
string_buffer += my_file_text_reader.read(1) # read one Unicode char at a time
# binary data must be next. Where do we get the binary length from?
print string_buffer
data = my_file_buffer.read(3)
print data
string_buffer = ""
A quicker, less extensible way might be to use the approach you've suggested in your question by intelligently parsing the text portions, reading each UTF-8 sequence of bytes at a time. The following code (from http://rosettacode.org/wiki/Read_a_file_character_by_character/UTF8#Python), seems to be a neat way to conservatively read UTF-8 bytes into characters from a binary file:
def get_next_character(f):
# note: assumes valid utf-8
c = f.read(1)
while c:
while True:
try:
yield c.decode('utf-8')
except UnicodeDecodeError:
# we've encountered a multibyte character
# read another byte and try again
c += f.read(1)
else:
# c was a valid char, and was yielded, continue
c = f.read(1)
break
# Usage:
with open("input.txt","rb") as f:
my_unicode_str = ""
for c in get_next_character(f):
my_unicode_str += c

python, crawler for website, stored the jpg and png files, but can't be opend. why?

win8.1-32bit, python3.4
made a web-robot for www.douban.com to get the main html, jpg files and png files.
but when finished, I can't open the pic files.(Windows Photo Viewer can't open this picture balablabala~~~~)
Questions:
1: why can't the pics be opened?
2: if line 35 is edited like this:dbr.write(data), the command line will prompt: TypeError: 'str' does not support the buffer interface.
Same thing will happen for line 51 and 59.
But when line 35 is :dbr.write(bytes(data, 'UTF-8')) , I will get the right html file. So I did the same for line 51 and 59 for pic files, but somethings went wrong. I wonder there should be a bug in the "write()", but I can't figure out what exactly is wrong.
Here is the code.
import urllib.request
import os
import re
#make dirs for douban_robot, jpg, png
dirpath = 'D:/Pwork/webrobot/'
if not os.path.isdir(dirpath):
os.makedirs(dirpath)
jpg_path = dirpath + 'jpgfiles/'
png_path = dirpath + 'pngfiles/'
if not os.path.isdir(jpg_path):
os.makedirs(jpg_path)
if not os.path.isdir(png_path):
os.makedirs(png_path)
douban_robot = dirpath + 'douban.html'
url = 'http://www.douban.com'
#get .html
data = urllib.request.urlopen(url).read().decode('UTF-8')
with open(douban_robot, 'wb') as dbr:
dbr.write(bytes(data, 'UTF-8'))
dbr.close()
# create regex
re_jpg = re.compile(r'<img src="(http.+?.jpg)"')
re_png = re.compile(r'<img src="(http:.+?.png)"')
jpg_data = re_jpg.findall(data)
png_data = re_png.findall(data)
# for test jpg and png date
print(jpg_data, png_data)
#get jpg files
i = 1
for image in jpg_data:
jpg_name = jpg_path + str(i)+'.jpg'
#urllib.request.urlretrieve(image, jpg_name)
with open(jpg_name, 'wb') as jpg_file:
jpg_file.write(bytes(image, 'UTF-8'))
jpg_file.close()
i += 1
for image in png_data:
png_name = png_path + str(i)+'.png'
#urllib.request.urlretrieve(image, png_name)
with open(png_name, 'wb') as png_file:
png_file.write(bytes(image, 'UTF-8'))
png_file.close()
i += 1

The variables jpg_data and png_data are lists containing captured URLs. Your loops iterate over each URL, placing the URL string in the variable image. Then, in both loops, you write the URL string to the file, not the actual image. It actually looks like the commented out urllib lines would do the trick, instead of what you're currently doing now.
The .write() function expects you to give it an object that matches the mode of the file. When you call open(..., 'wb'), you're saying to open the file in write and binary mode, which means that you need to give it bytes instead of str.
Bytes are the fundamental way everything is stored in a computer. Everything is a series of bytes -- the data on your hard drive, and the data you send and receive on the Internet. Bytes don't really have meaning on their own -- each one is just 8 bits strung together. The meaning depends on how you interpret the bytes. For instance, you could interpret a single byte as representing a number from 0 to 255. Or, you could interpret it as a number from -128 to 127 (both of these are common). You could also assign these "numbers" to characters, and interpret a sequence of bytes as text. However, this only allows you to represent 256 characters, and there are many more than that in the world's various languages. So, there are multiple ways of representing text as sequences of bytes. These are called "character encodings". The most popular modern one is "UTF-8".
In Python, a bytes object is just a series of bytes. It has no special meaning -- nobody has said what it represents yet. If you want to use that as text, you need to decode it, using one of the character encodings. Once you do that (.decode('UTF-8')), you have a str object. In order to write it to disk (or the network), your str will have to eventually be encoded back into bytes. When you open a file in text mode, Python chooses your computer's default encoding, and it will decode everything you read using that, and encode everything you write with it. However, when you open a file in b mode, Python expects that you will give it bytes, and so it throws an error when you give it a str instead. Since you know the HTML file you downloaded and put in data is text, it would have been best for you to save it to a file in text mode. However, encoding it as UTF-8 and writing it to a binary file works too, as long as your system's default encoding is UTF-8. In general, when you have a str and you want to write it to a file, open the file in text mode (just don't pass b in the mode parameter) and let Python pick the encoding, since it knows better than you do!
For more info on the character sets and encoding stuff (which I only glossed over), you really should read this article.

Stop python from writing a carriage return when hex value is 0x0A

I decided to brush up on my python, and for the first project I thought I would write a script to help me with some homework for another class I have. For this class, I have an excel spread sheet that converts some data to hex. I would normally have to manually type out the hex values into the program I'm using or I could load the binary data from a file.
The script I have set up right now lets me copy the section in the spread sheet and copy the contents to a temporary text file. When I run my script it creates a file with the binary data. It works except for when I have a hex value of 0x0A, because of the way I convert the string value to hex converts it to '\n' so the binary file has 0D 0A rather then just 0A.
The way I get the hex value:
hexvalue = chr(int(string_value,16))
The way I write to the file:
f = file("code_out", "w")
for byte in data:
f.write(byte)
f.close()
What's the proper way of doing this?

I think you need to open the file for binary writing!
f = open('file', 'wb')

Open the file in "binary mode"
On Windows, 'b' appended to the mode opens the file in binary mode, so there are also modes like 'rb', 'wb', and 'r+b'. Python on Windows makes a distinction between text and binary files; the end-of-line characters in text files are automatically altered slightly when data is read or written.
That is, under non-"binary mode" in Windows, when a "\n" (LF, \x0A) is written to the file stream the actual result is that the byte sequence "\r\n" (CR LF, \x0D \x0A) is written. See newline for additional notes.
This behind-the-scenes modification to file data is fine for ASCII text files, but it’ll corrupt binary data like that in JPEG or EXE files. Be very careful to use binary mode when reading and writing such files. On Unix, it doesn’t hurt to append a 'b' to the mode, so you can use it platform-independently for all binary files.