We Keep Coding

'utf-8' codec can't decode byte 0xe1: unexpected end of data [duplicate]

I am quite confused about the concept of character encoding.
What is Unicode, GBK, etc? How does a programming language use them?
Do I need to bother knowing about them? Is there a simpler or faster way of programming without having to trouble myself with them?

ASCII is fundamental
Originally 1 character was always stored as 1 byte. A byte (8 bits) has the potential to distinct 256 possible values. But in fact only the first 7 bits were used. So only 128 characters were defined. This set is known as the ASCII character set.
0x00 - 0x1F contain steering codes (e.g. CR, LF, STX, ETX, EOT, BEL, ...)
0x20 - 0x40 contain numbers and punctuation
0x41 - 0x7F contain mostly alphabetic characters
0x80 - 0xFF the 8th bit = undefined.
French, German and many other languages needed additional characters. (e.g. à, é, ç, ô, ...) which were not available in the ASCII character set. So they used the 8th bit to define their characters. This is what is known as "extended ASCII".
The problem is that the additional 1 bit has not enough capacity to cover all languages in the world. So each region has its own ASCII variant. There are many extended ASCII encodings (latin-1 being a very popular one).
Popular question: "Is ASCII a character set or is it an encoding" ? ASCII is a character set. However, in programming charset and encoding are wildly used as synonyms. If I want to refer to an encoding that only contains the ASCII characters and nothing more (the 8th bit is always 0): that's US-ASCII.
Unicode goes one step further
Unicode is a great example of a character set - not an encoding. It uses the same characters like the ASCII standard, but it extends the list with additional characters, which gives each character a codepoint in format u+xxxx. It has the ambition to contain all characters (and popular icons) used in the entire world.
UTF-8, UTF-16 and UTF-32 are encodings that apply the Unicode character table. But they each have a slightly different way on how to encode them. UTF-8 will only use 1 byte when encoding an ASCII character, giving the same output as any other ASCII encoding. But for other characters, it will use the first bit to indicate that a 2nd byte will follow.
GBK is an encoding, which just like UTF-8 uses multiple bytes. The principle is pretty much the same. The first byte follows the ASCII standard, so only 7 bits are used. But just like with UTF-8, The 8th bit can be used to indicate the presence of a 2nd byte, which it then uses to encode one of 22,000 Chinese characters. The main difference, is that this does not follow the Unicode character set, by contrast it uses some Chinese character set.
Decoding data
When you encode your data, you use an encoding, but when you decode data, you will need to know what encoding was used, and use that same encoding to decode it.
Unfortunately, encodings aren't always declared or specified. It would have been ideal if all files contained a prefix to indicate what encoding their data was stored in. But still in many cases applications just have to assume or guess what encoding they should use. (e.g. they use the standard encoding of the operating system).
There still is a lack of awareness about this, as still many developers don't even know what an encoding is.
Mime types
Mime types are sometimes confused with encodings. They are a useful way for the receiver to identify what kind of data is arriving. Here is an example, of how the HTTP protocol defines it's content type using a mime type declaration.
Content-Type: text/html; charset=utf-8
And that's another great source of confusion. A mime type describes what kind of data a message contains (e.g. text/xml, image/png, ...). And in some cases it will additionally also describe how the data is encoded (i.e. charset=utf-8). 2 points of confusion:
Not all mime types declare an encoding. In some cases it is only optional or sometimes completely pointless.
The syntax charset=utf-8 adds up to the semantic confusion, because as explained earlier, UTF-8 is an encoding and not a character set. But as explained earlier, some people just use the 2 words interchangeably.
For example, in the case of text/xml it would be pointless to declare an encoding (and a charset parameter would simply be ignored). Instead, XML parsers in general will read the first line of the file, looking for the <?xml encoding=... tag. If it's there, then they will reopen the file using that encoding.
The same problem exists when sending e-mails. An e-mail can contain a html message or just plain text. Also in that case mime types are used to define the type of the content.
But in summary, a mime type isn't always sufficient to solve the problem.
Data types in programming languages
In case of Java (and many other programming languages) in addition to the dangers of encodings, there's also the complexity of casting bytes and integers to characters because their content is stored in different ranges.
a byte is stored as a signed byte (range: -128 to 127).
the char type in java is stored in 2 unsigned bytes (range: 0 - 65535)
a stream returns an integer in range -1 to 255.
If you know that your data only contains ASCII values. Then with the proper skill you can parse your data from bytes to characters or wrap them immediately in Strings.
// the -1 indicates that there is no data
int input = stream.read();
if (input == -1) throw new EOFException();
// bytes must be made positive first.
byte myByte = (byte) input;
int unsignedInteger = myByte & 0xFF;
char ascii = (char)(unsignedInteger);
Shortcuts
The shortcut in java is to use readers and writers and to specify the encoding when you instantiate them.
// wrap your stream in a reader.
// specify the encoding
// The reader will decode the data for you
Reader reader = new InputStreamReader(inputStream, StandardCharsets.UTF_8);
As explained earlier for XML files it doesn't matter that much, because any decent DOM or JAXB marshaller will check for an encoding attribute.

(Note that I'm using some of these terms loosely/colloquially for a simpler explanation that still hits the key points.)
A byte can only have 256 distinct values, being 8 bits.
Since there are character sets with more than 256 characters in the character set one cannot in general simply say that each character is a byte.
Therefore, there must be mappings that describe how to turn each character in a character set into a sequence of bytes. Some characters might be mapped to a single byte but others will have to be mapped to multiple bytes.
Those mappings are encodings, because they are telling you how to encode characters into sequences of bytes.
As for Unicode, at a very high level, Unicode is an attempt to assign a single, unique number to every character. Obviously that number has to be something wider than a byte since there are more than 256 characters :) Java uses a version of Unicode where every character is assigned a 16-bit value (and this is why Java characters are 16 bits wide and have integer values from 0 to 65535). When you get the byte representation of a Java character, you have to tell the JVM the encoding you want to use so it will know how to choose the byte sequence for the character.

Character encoding is what you use to solve the problem of writing software for somebody who uses a different language than you do.
You don't know how what the characters are and how they are ordered. Therefore, you don't know what the strings in this new language will look like in binary and frankly, you don't care.
What you do have is a way of translating strings from the language you speak to the language they speak (say a translator). You now need a system that is capable of representing both languages in binary without conflicts. The encoding is that system.
It is what allows you to write software that works regardless of the way languages are represented in binary.

Most computer programs must communicate with a person using some text in a natural language (a language used by humans). But computers have no fundamental means for representing text: the fundamental computer representation is a sequence of bits organized into bytes and words, with hardware support for interpreting sequences of bits as fixed width base-2 (binary) integers and floating-point real numbers. Computer programs must therefore have a scheme for representing text as sequences of bits. This is fundamentally what character encoding is. There is no inherently obvious or correct scheme for character encoding, and so there exist many possible character encodings.
However, practical character encodings have some shared characteristics.
Encoded texts are divided into a sequence of characters (graphemes).
Each of the known possible characters has an encoding. The encoding of a text consists of the sequence of the encoding of the characters of the text.
Each possible (allowed) character is assigned a unique unsigned (non negative) integer (this is sometimes called a code point). Texts are therefore encoded as a sequence of unsigned integers. Different character encodings differ in the characters they allow, and how they assign these unique integers. Most character encodings do not allow all the characters used by the many human writing systems (scripts) that do and have existed. Thus character encodings differ in which texts they can represent at all. Even character encodings that can represent the same text can represent it differently, because of their different assignment of code points.
The unsigned integer encoding a character is encoded as a sequence of bits. Character encodings differ in the number of bits they use for this encoding. When those bits are grouped into bytes (as is the case for popular encodings), character encodings can differ in endianess. Character encodings can differ in whether they are fixed width (the same number of bits for each encoded character) or variable width (using more bits for some characters).
Therefore, if a computer program receives a sequence of bytes that are meant to represent some text, the computer program must know the character encoding used for that text, if it is to do any kind of manipulation of that text (other than regarding it as an opaque value and forwarding it unchanged). The only possibilities are that the text is accompanied by additional data that indicates the encoding used or the program requires (assumes) that the text has a particular encoding.
Similarly, if a computer program must send (output) text to another program or a display device, it must either tell the destination the character encoding used or the program must use the encoding that the destination expects.
In practice, almost all problems with character encodings are caused when a destination expects text sent using one character encoding, and the text is actually sent with a different character encoding. That in turn is typically caused by the computer programmer not bearing in mind that there exist many possible character encodings, and that their program can not treat encoded text as opaque values, but must convert from an external representation on input and convert to an external representation on output.

UnicodeDecodeError: 'utf-8' codec can't decode byte 0xfc in position Pandas [duplicate]

I am quite confused about the concept of character encoding.
What is Unicode, GBK, etc? How does a programming language use them?
Do I need to bother knowing about them? Is there a simpler or faster way of programming without having to trouble myself with them?

ASCII is fundamental
Originally 1 character was always stored as 1 byte. A byte (8 bits) has the potential to distinct 256 possible values. But in fact only the first 7 bits were used. So only 128 characters were defined. This set is known as the ASCII character set.
0x00 - 0x1F contain steering codes (e.g. CR, LF, STX, ETX, EOT, BEL, ...)
0x20 - 0x40 contain numbers and punctuation
0x41 - 0x7F contain mostly alphabetic characters
0x80 - 0xFF the 8th bit = undefined.
French, German and many other languages needed additional characters. (e.g. à, é, ç, ô, ...) which were not available in the ASCII character set. So they used the 8th bit to define their characters. This is what is known as "extended ASCII".
The problem is that the additional 1 bit has not enough capacity to cover all languages in the world. So each region has its own ASCII variant. There are many extended ASCII encodings (latin-1 being a very popular one).
Popular question: "Is ASCII a character set or is it an encoding" ? ASCII is a character set. However, in programming charset and encoding are wildly used as synonyms. If I want to refer to an encoding that only contains the ASCII characters and nothing more (the 8th bit is always 0): that's US-ASCII.
Unicode goes one step further
Unicode is a great example of a character set - not an encoding. It uses the same characters like the ASCII standard, but it extends the list with additional characters, which gives each character a codepoint in format u+xxxx. It has the ambition to contain all characters (and popular icons) used in the entire world.
UTF-8, UTF-16 and UTF-32 are encodings that apply the Unicode character table. But they each have a slightly different way on how to encode them. UTF-8 will only use 1 byte when encoding an ASCII character, giving the same output as any other ASCII encoding. But for other characters, it will use the first bit to indicate that a 2nd byte will follow.
GBK is an encoding, which just like UTF-8 uses multiple bytes. The principle is pretty much the same. The first byte follows the ASCII standard, so only 7 bits are used. But just like with UTF-8, The 8th bit can be used to indicate the presence of a 2nd byte, which it then uses to encode one of 22,000 Chinese characters. The main difference, is that this does not follow the Unicode character set, by contrast it uses some Chinese character set.
Decoding data
When you encode your data, you use an encoding, but when you decode data, you will need to know what encoding was used, and use that same encoding to decode it.
Unfortunately, encodings aren't always declared or specified. It would have been ideal if all files contained a prefix to indicate what encoding their data was stored in. But still in many cases applications just have to assume or guess what encoding they should use. (e.g. they use the standard encoding of the operating system).
There still is a lack of awareness about this, as still many developers don't even know what an encoding is.
Mime types
Mime types are sometimes confused with encodings. They are a useful way for the receiver to identify what kind of data is arriving. Here is an example, of how the HTTP protocol defines it's content type using a mime type declaration.
Content-Type: text/html; charset=utf-8
And that's another great source of confusion. A mime type describes what kind of data a message contains (e.g. text/xml, image/png, ...). And in some cases it will additionally also describe how the data is encoded (i.e. charset=utf-8). 2 points of confusion:
Not all mime types declare an encoding. In some cases it is only optional or sometimes completely pointless.
The syntax charset=utf-8 adds up to the semantic confusion, because as explained earlier, UTF-8 is an encoding and not a character set. But as explained earlier, some people just use the 2 words interchangeably.
For example, in the case of text/xml it would be pointless to declare an encoding (and a charset parameter would simply be ignored). Instead, XML parsers in general will read the first line of the file, looking for the <?xml encoding=... tag. If it's there, then they will reopen the file using that encoding.
The same problem exists when sending e-mails. An e-mail can contain a html message or just plain text. Also in that case mime types are used to define the type of the content.
But in summary, a mime type isn't always sufficient to solve the problem.
Data types in programming languages
In case of Java (and many other programming languages) in addition to the dangers of encodings, there's also the complexity of casting bytes and integers to characters because their content is stored in different ranges.
a byte is stored as a signed byte (range: -128 to 127).
the char type in java is stored in 2 unsigned bytes (range: 0 - 65535)
a stream returns an integer in range -1 to 255.
If you know that your data only contains ASCII values. Then with the proper skill you can parse your data from bytes to characters or wrap them immediately in Strings.
// the -1 indicates that there is no data
int input = stream.read();
if (input == -1) throw new EOFException();
// bytes must be made positive first.
byte myByte = (byte) input;
int unsignedInteger = myByte & 0xFF;
char ascii = (char)(unsignedInteger);
Shortcuts
The shortcut in java is to use readers and writers and to specify the encoding when you instantiate them.
// wrap your stream in a reader.
// specify the encoding
// The reader will decode the data for you
Reader reader = new InputStreamReader(inputStream, StandardCharsets.UTF_8);
As explained earlier for XML files it doesn't matter that much, because any decent DOM or JAXB marshaller will check for an encoding attribute.

(Note that I'm using some of these terms loosely/colloquially for a simpler explanation that still hits the key points.)
A byte can only have 256 distinct values, being 8 bits.
Since there are character sets with more than 256 characters in the character set one cannot in general simply say that each character is a byte.
Therefore, there must be mappings that describe how to turn each character in a character set into a sequence of bytes. Some characters might be mapped to a single byte but others will have to be mapped to multiple bytes.
Those mappings are encodings, because they are telling you how to encode characters into sequences of bytes.
As for Unicode, at a very high level, Unicode is an attempt to assign a single, unique number to every character. Obviously that number has to be something wider than a byte since there are more than 256 characters :) Java uses a version of Unicode where every character is assigned a 16-bit value (and this is why Java characters are 16 bits wide and have integer values from 0 to 65535). When you get the byte representation of a Java character, you have to tell the JVM the encoding you want to use so it will know how to choose the byte sequence for the character.

Character encoding is what you use to solve the problem of writing software for somebody who uses a different language than you do.
You don't know how what the characters are and how they are ordered. Therefore, you don't know what the strings in this new language will look like in binary and frankly, you don't care.
What you do have is a way of translating strings from the language you speak to the language they speak (say a translator). You now need a system that is capable of representing both languages in binary without conflicts. The encoding is that system.
It is what allows you to write software that works regardless of the way languages are represented in binary.

Most computer programs must communicate with a person using some text in a natural language (a language used by humans). But computers have no fundamental means for representing text: the fundamental computer representation is a sequence of bits organized into bytes and words, with hardware support for interpreting sequences of bits as fixed width base-2 (binary) integers and floating-point real numbers. Computer programs must therefore have a scheme for representing text as sequences of bits. This is fundamentally what character encoding is. There is no inherently obvious or correct scheme for character encoding, and so there exist many possible character encodings.
However, practical character encodings have some shared characteristics.
Encoded texts are divided into a sequence of characters (graphemes).
Each of the known possible characters has an encoding. The encoding of a text consists of the sequence of the encoding of the characters of the text.
Each possible (allowed) character is assigned a unique unsigned (non negative) integer (this is sometimes called a code point). Texts are therefore encoded as a sequence of unsigned integers. Different character encodings differ in the characters they allow, and how they assign these unique integers. Most character encodings do not allow all the characters used by the many human writing systems (scripts) that do and have existed. Thus character encodings differ in which texts they can represent at all. Even character encodings that can represent the same text can represent it differently, because of their different assignment of code points.
The unsigned integer encoding a character is encoded as a sequence of bits. Character encodings differ in the number of bits they use for this encoding. When those bits are grouped into bytes (as is the case for popular encodings), character encodings can differ in endianess. Character encodings can differ in whether they are fixed width (the same number of bits for each encoded character) or variable width (using more bits for some characters).
Therefore, if a computer program receives a sequence of bytes that are meant to represent some text, the computer program must know the character encoding used for that text, if it is to do any kind of manipulation of that text (other than regarding it as an opaque value and forwarding it unchanged). The only possibilities are that the text is accompanied by additional data that indicates the encoding used or the program requires (assumes) that the text has a particular encoding.
Similarly, if a computer program must send (output) text to another program or a display device, it must either tell the destination the character encoding used or the program must use the encoding that the destination expects.
In practice, almost all problems with character encodings are caused when a destination expects text sent using one character encoding, and the text is actually sent with a different character encoding. That in turn is typically caused by the computer programmer not bearing in mind that there exist many possible character encodings, and that their program can not treat encoded text as opaque values, but must convert from an external representation on input and convert to an external representation on output.

How to display Chinese characters in Python? [duplicate]

I am quite confused about the concept of character encoding.
What is Unicode, GBK, etc? How does a programming language use them?
Do I need to bother knowing about them? Is there a simpler or faster way of programming without having to trouble myself with them?

ASCII is fundamental
Originally 1 character was always stored as 1 byte. A byte (8 bits) has the potential to distinct 256 possible values. But in fact only the first 7 bits were used. So only 128 characters were defined. This set is known as the ASCII character set.
0x00 - 0x1F contain steering codes (e.g. CR, LF, STX, ETX, EOT, BEL, ...)
0x20 - 0x40 contain numbers and punctuation
0x41 - 0x7F contain mostly alphabetic characters
0x80 - 0xFF the 8th bit = undefined.
French, German and many other languages needed additional characters. (e.g. à, é, ç, ô, ...) which were not available in the ASCII character set. So they used the 8th bit to define their characters. This is what is known as "extended ASCII".
The problem is that the additional 1 bit has not enough capacity to cover all languages in the world. So each region has its own ASCII variant. There are many extended ASCII encodings (latin-1 being a very popular one).
Popular question: "Is ASCII a character set or is it an encoding" ? ASCII is a character set. However, in programming charset and encoding are wildly used as synonyms. If I want to refer to an encoding that only contains the ASCII characters and nothing more (the 8th bit is always 0): that's US-ASCII.
Unicode goes one step further
Unicode is a great example of a character set - not an encoding. It uses the same characters like the ASCII standard, but it extends the list with additional characters, which gives each character a codepoint in format u+xxxx. It has the ambition to contain all characters (and popular icons) used in the entire world.
UTF-8, UTF-16 and UTF-32 are encodings that apply the Unicode character table. But they each have a slightly different way on how to encode them. UTF-8 will only use 1 byte when encoding an ASCII character, giving the same output as any other ASCII encoding. But for other characters, it will use the first bit to indicate that a 2nd byte will follow.
GBK is an encoding, which just like UTF-8 uses multiple bytes. The principle is pretty much the same. The first byte follows the ASCII standard, so only 7 bits are used. But just like with UTF-8, The 8th bit can be used to indicate the presence of a 2nd byte, which it then uses to encode one of 22,000 Chinese characters. The main difference, is that this does not follow the Unicode character set, by contrast it uses some Chinese character set.
Decoding data
When you encode your data, you use an encoding, but when you decode data, you will need to know what encoding was used, and use that same encoding to decode it.
Unfortunately, encodings aren't always declared or specified. It would have been ideal if all files contained a prefix to indicate what encoding their data was stored in. But still in many cases applications just have to assume or guess what encoding they should use. (e.g. they use the standard encoding of the operating system).
There still is a lack of awareness about this, as still many developers don't even know what an encoding is.
Mime types
Mime types are sometimes confused with encodings. They are a useful way for the receiver to identify what kind of data is arriving. Here is an example, of how the HTTP protocol defines it's content type using a mime type declaration.
Content-Type: text/html; charset=utf-8
And that's another great source of confusion. A mime type describes what kind of data a message contains (e.g. text/xml, image/png, ...). And in some cases it will additionally also describe how the data is encoded (i.e. charset=utf-8). 2 points of confusion:
Not all mime types declare an encoding. In some cases it is only optional or sometimes completely pointless.
The syntax charset=utf-8 adds up to the semantic confusion, because as explained earlier, UTF-8 is an encoding and not a character set. But as explained earlier, some people just use the 2 words interchangeably.
For example, in the case of text/xml it would be pointless to declare an encoding (and a charset parameter would simply be ignored). Instead, XML parsers in general will read the first line of the file, looking for the <?xml encoding=... tag. If it's there, then they will reopen the file using that encoding.
The same problem exists when sending e-mails. An e-mail can contain a html message or just plain text. Also in that case mime types are used to define the type of the content.
But in summary, a mime type isn't always sufficient to solve the problem.
Data types in programming languages
In case of Java (and many other programming languages) in addition to the dangers of encodings, there's also the complexity of casting bytes and integers to characters because their content is stored in different ranges.
a byte is stored as a signed byte (range: -128 to 127).
the char type in java is stored in 2 unsigned bytes (range: 0 - 65535)
a stream returns an integer in range -1 to 255.
If you know that your data only contains ASCII values. Then with the proper skill you can parse your data from bytes to characters or wrap them immediately in Strings.
// the -1 indicates that there is no data
int input = stream.read();
if (input == -1) throw new EOFException();
// bytes must be made positive first.
byte myByte = (byte) input;
int unsignedInteger = myByte & 0xFF;
char ascii = (char)(unsignedInteger);
Shortcuts
The shortcut in java is to use readers and writers and to specify the encoding when you instantiate them.
// wrap your stream in a reader.
// specify the encoding
// The reader will decode the data for you
Reader reader = new InputStreamReader(inputStream, StandardCharsets.UTF_8);
As explained earlier for XML files it doesn't matter that much, because any decent DOM or JAXB marshaller will check for an encoding attribute.

(Note that I'm using some of these terms loosely/colloquially for a simpler explanation that still hits the key points.)
A byte can only have 256 distinct values, being 8 bits.
Since there are character sets with more than 256 characters in the character set one cannot in general simply say that each character is a byte.
Therefore, there must be mappings that describe how to turn each character in a character set into a sequence of bytes. Some characters might be mapped to a single byte but others will have to be mapped to multiple bytes.
Those mappings are encodings, because they are telling you how to encode characters into sequences of bytes.
As for Unicode, at a very high level, Unicode is an attempt to assign a single, unique number to every character. Obviously that number has to be something wider than a byte since there are more than 256 characters :) Java uses a version of Unicode where every character is assigned a 16-bit value (and this is why Java characters are 16 bits wide and have integer values from 0 to 65535). When you get the byte representation of a Java character, you have to tell the JVM the encoding you want to use so it will know how to choose the byte sequence for the character.

Character encoding is what you use to solve the problem of writing software for somebody who uses a different language than you do.
You don't know how what the characters are and how they are ordered. Therefore, you don't know what the strings in this new language will look like in binary and frankly, you don't care.
What you do have is a way of translating strings from the language you speak to the language they speak (say a translator). You now need a system that is capable of representing both languages in binary without conflicts. The encoding is that system.
It is what allows you to write software that works regardless of the way languages are represented in binary.

Most computer programs must communicate with a person using some text in a natural language (a language used by humans). But computers have no fundamental means for representing text: the fundamental computer representation is a sequence of bits organized into bytes and words, with hardware support for interpreting sequences of bits as fixed width base-2 (binary) integers and floating-point real numbers. Computer programs must therefore have a scheme for representing text as sequences of bits. This is fundamentally what character encoding is. There is no inherently obvious or correct scheme for character encoding, and so there exist many possible character encodings.
However, practical character encodings have some shared characteristics.
Encoded texts are divided into a sequence of characters (graphemes).
Each of the known possible characters has an encoding. The encoding of a text consists of the sequence of the encoding of the characters of the text.
Each possible (allowed) character is assigned a unique unsigned (non negative) integer (this is sometimes called a code point). Texts are therefore encoded as a sequence of unsigned integers. Different character encodings differ in the characters they allow, and how they assign these unique integers. Most character encodings do not allow all the characters used by the many human writing systems (scripts) that do and have existed. Thus character encodings differ in which texts they can represent at all. Even character encodings that can represent the same text can represent it differently, because of their different assignment of code points.
The unsigned integer encoding a character is encoded as a sequence of bits. Character encodings differ in the number of bits they use for this encoding. When those bits are grouped into bytes (as is the case for popular encodings), character encodings can differ in endianess. Character encodings can differ in whether they are fixed width (the same number of bits for each encoded character) or variable width (using more bits for some characters).
Therefore, if a computer program receives a sequence of bytes that are meant to represent some text, the computer program must know the character encoding used for that text, if it is to do any kind of manipulation of that text (other than regarding it as an opaque value and forwarding it unchanged). The only possibilities are that the text is accompanied by additional data that indicates the encoding used or the program requires (assumes) that the text has a particular encoding.
Similarly, if a computer program must send (output) text to another program or a display device, it must either tell the destination the character encoding used or the program must use the encoding that the destination expects.
In practice, almost all problems with character encodings are caused when a destination expects text sent using one character encoding, and the text is actually sent with a different character encoding. That in turn is typically caused by the computer programmer not bearing in mind that there exist many possible character encodings, and that their program can not treat encoded text as opaque values, but must convert from an external representation on input and convert to an external representation on output.

Base64 conversion decimals

I've been reading about base64 conversion, and what I understand is that the encoded version of the original data will be 133% of the original size.
Then, I'm reading about how YouTube is able to have unique identifiers to their videos like FJZQSHn7fc and the reason was: an 11 character base64 string can map to a huge number.
Wait, say a huge number contains 20 characters, then wouldn't a base64 encoded string be 133% of that size, not shorter?
I'm very confused. Are there different types of base64 conversion (string to base64 vs. decimal to base64), once resulting in a bigger, and the other in a smaller resulting string?

Each character in base 64 can encode 6 bits of data. Thus 11 characters can encode 6x11 = 66 bits of data.
2^66 = 73786976294838206464
73786976294838206464 (approximately 7.4 x 10^19 or 74 quintillion) possible identifiers is more than enough to distinguish unique YouTube videos for the foreseeable future.
It is unlikely that YouTube is using these strings of length 11 as encodings of smaller objects. You can use base64 (just a number in base 64 after all) without having to think of it as an encoding of something else, just like you can use bytes (binary numbers with 8 bits) without thinking of those bytes as being encodings of ascii characters. The only important question with an identifier scheme is if there are enough identifiers to go around. In this case there clearly are.

Think of it like this: you have a 64bit number (called long in Java, for example).
Now, you can print that number in different ways:
As a binary number (base 2), printing 64 '0' or '1'
As a decimal number (base 10), printing up to 20 decimal digits
As a hexadecimal number (base 16), printing 16 hexadeciaml digits
As a number in base 64, printing 11 "digits" in that base. You can use any graphical symbols as digits.
... you understand by now that there are many more possibilities ...
It seems like they use the same base-64 numbers as the ones that are used in base64 encoding, that is, uppercase and lowercase letters, ordinary digits and 2 extra chars. Each character represents a 6-bit value. So you get 66 bits, and depending on the algorithm used, either the leading or trailing 2 bits are cut off to get a nice long value back.

You are confusing what things are being compared.
There are 2 statements, both comparing different things:
"base64 encoding is 133% bigger than original size"
"An 11 character base64 string can encode a huge number"
In the case of 1, they are normally referring to a string encoded maybe with ASCII using 8bits a character, and comparing that with the same string encoded in base64. That is 133% bigger, because in base64 you can't use all 255 bit combinations in every byte.
In the case of 2, they are comparing using a numeric identifier, and then either encoding it as base64, or base10. In this case, base64 is a lot shorter than base10.
You can also think of the (1) case as comparing base256 against base64, and the (2) case as comparing base10 against base64.

When you say Base64, some would think of RFC 4648. If YouTube is using RFC 4648, then it's a 12-digit number where they're omitting the last digit because it is always '=', the padding character (the 65th element of the base64 alphabet). The 12 digits represent three blocks of four digits, and four digits yield 24 bits of information. YouTube video IDs would therefore be 64-bit, not 66-bit, if they're using the standard.
Those 64 bits might be representing an unsigned integer. YouTube used MySQL and then sharded MySQL through Vitess, so you could imagine them using an UNSIGNED BIGINT key internally that they encode via RFC 4648-compliant Base64 externally.
Clearly Tom Scott thinks YouTube is squeezing 66 bits out of their 11 characters; his video says so.
If he's wrong, then their frontend might allow you to specify four distinct video IDs for the same video. Those two extra bits' values do not affect the UNSIGNED BIGINT. Which two bits they are depend on endianness and other choices of encoding.
Regardless of whether YouTube is using standard or nonstandard encoding, they can represent 18446744073709551615 in 11 characters (since the padding character is always there and and thus omitted for a 64-bit quantity).
Perhaps they use something like the following to compute a pseudorandom 64-bit integer when a new video is created:
import base64
import random
def Base64RandomSlug():
array = bytearray(random.getrandbits(8) for x in range(64 // 8))
b = base64.urlsafe_b64encode(bytes(array))
return b.decode('utf-8').rstrip('=')

LZ77 compression reserved bytes "< , >"

I'm learning about LZ77 compression, and I saw that when I find a repeated string of bytes, I can use a pointer of the form <distance, length>, and that the "<", ",", ">" bytes are reserved. So... How do I compress a file that has these bytes, if I cannot compress these byte,s but cannot change it by a different byte (because decoders wouldn't be able to read it). Is there a way? Or decoders only decode is there is a exact <d, l> string? (if there is, so imagine if by a coencidence, we find these bytes in a file. What would happen?)
Thanks!

LZ77 is about referencing strings back in the decompressing buffer by their lengths and distances from the current position. But it is left to you how do you encode these back-references. Many implementations of LZ77 do it in different ways.
But you are right that there must be some way to distinguish "literals" (uncompressed pieces of data meant to be copied "as is" from the input to the output) from "back-references" (which are copied from already uncompressed portion).
One way to do it is reserving some characters as "special" (so called "escape sequences"). You can do it the way you did it, that is, by using < to mark the start of a back-reference. But then you also need a way to output < if it is a literal. You can do it, for example, by establishing that when after < there's another <, then it means a literal, and you just output one <. Or, you can establish that if after < there's immediately >, with nothing in between, then that's not a back-reference, so you just output <.
It also wouldn't be the most efficient way to encode those back-references, because it uses several bytes to encode a back-reference, so it will become efficient only for referencing strings longer than those several bytes. For shorter back-references it will inflate the data instead of compressing them, unless you establish that matches shorter than several bytes are being left as is, instead of generating back-references. But again, this means lower compression gains.
If you compress only plain old ASCII texts, you can employ a better encoding scheme, because ASCII uses just 7 out of 8 bits in a byte. So you can use the highest bit to signal a back-reference, and then use the remaining 7 bits as length, and the very next byte (or two) as back-reference's distance. This way you can always tell for sure whether the next byte is a literal ASCII character or a back-reference, by checking its highest bit. If it is 0, just output the character as is. If it is 1, use the following 7 bits as length, and read up the next 2 bytes to use it as distance. This way every back-reference takes 3 bytes, so you can efficiently compress text files with repeating sequences of more than 3 characters long.
But there's a still better way to do this, which gives even more compression: you can replace your characters with bit codes of variable lengths, crafted in such a way that the characters appearing more often would have shortest codes, and those which are rare would have longer codes. To achieve that, these codes have to be so-called "prefix codes", so that no code would be a prefix of some other code. When your codes have this property, you can always distinguish them by reading these bits in sequence until you decode some of them. Then you can be sure that you won't get any other valid item by reading more bits. The next bit always starts another new sequence. To produce such codes, you need to use Huffman trees. You can then join all your bytes and different lengths of references into one such tree and generate distinct bit codes for them, depending on their frequency. When you try to decode them, you just read the bits until you reach the code of some of these elements, and then you know for sure whether it is a code of some literal character or a code for back-reference's length. In the second case, you then read some additional bits for the distance of the back-reference (also encoded with a prefix code). This is what DEFLATE compression scheme does. But this is whole another story, and you will find the details in the RFC supplied by #MarkAdler.

If I understand your question correctly, it makes no sense. There are no "reserved bytes" for the uncompressed input of an LZ77 compressor. You need to simply encodes literals and length/distance pairs unambiguously.