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python3:input_output [2018/08/14 16:42]
jguerin Moved portion of analysis to footnote. |
python3:input_output [2018/08/14 19:04] (current)
jguerin |
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| ===== Input Basics ===== | ===== Input Basics ===== |
| Input in Python3 is handled via the ''%%input()%%'' function, and reads a newline-terminated string from standard input.((Unlike C++ and Java, input is line-based rather than token-based.)) Additional processing is done to the resulting string. | Input in Python3 is handled via the ''%%input()%%'' function, and reads a newline-terminated string from standard input.((Unlike C++ and Java, input is line-based rather than token-based.)) Any additional processing is done to the resulting string. |
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| <code python> | <code python> |
| ===== Advanced Input ===== | ===== Advanced Input ===== |
| ''input()'' will scale well for many easy and mid-level contest problems. For mid to upper problems with significant bounds on reads and writes ''input()'' will carry an increased risk of //time limit exceeded// judgements.((There is no guaranteed cutoff, but for many problems ''input()'' is //increasingly likely// to fail around 10<sup>3</sup>≤//n//≤10<sup>4</sup> lines.)) | ''input()'' will scale well for many easy and mid-level contest problems. For mid to upper problems with significant bounds on reads and writes ''input()'' will carry an increased risk of //time limit exceeded// judgements.((There is no guaranteed cutoff, but for many problems ''input()'' is //increasingly likely// to fail around 10<sup>3</sup>≤//n//≤10<sup>4</sup> lines.)) |
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| | === stdin.readline() === |
| | ''readline()'' is identical to the interface provided by ''input()'' except it //retains// the ''\n'' that is used to terminate the read.((This may require special handling in certain circumstance and can be safely ignored in others. E.g., ''.split()'' will //not// behave differently vs. ''input()''.)) |
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| <code python> | <code python> |
| </code> | </code> |
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| <code python> | |
| >>> from sys import * | |
| >>> x = stdin.readline().split() | |
| Hello World! # x=["Hello", "World!"] | |
| </code> | |
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| ''readlines()'' is stopped by an End Of File (EOF) character. You can send this from the terminal with <ctrl-D> | === stdin.readlines() === |
| | ''readlines()'' processes an entire file, terminated by an //end of file// character.((This behavior can be simulated on the terminal with ''<ctrl>+d''.)) |
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| <code python> | <code python> |
| To Everyone! # x=["Hello\n", "To Everyone!\n"] | To Everyone! # x=["Hello\n", "To Everyone!\n"] |
| </code> | </code> |
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| | ''<ctrl>+d'' would be used to terminate this example after the ''!''. |
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| | ''readlines()'' loads //and// stores an entire file into memory (as a list) its performance will exceed other options in Python3 for all but the most enormous files.((See the table below for an example where ''readlines()'' required storing ∼1GB of data.)) |
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| ==== Benchmarks ==== | ==== Benchmarks ==== |
| 10 characters per line (//n//= number of lines): | 10 characters per line (//n//= number of lines): |
| | //n// | input() | sys.stdin.readline() | sys.stdin.readlines() | | | //n// | input() | sys.stdin.readline() | sys.stdin.readlines() | |
| | 10<sup>4</sup> | .034 | .016 | .018 | | | 10<sup>4</sup> | .034s | .016s | .018s | |
| | 10<sup>5</sup> | .146 | .052 | .030 | | | 10<sup>5</sup> | .146s | .052s | .030s | |
| | 10<sup>6</sup> | 1.301 | .301 | .130 | | | 10<sup>6</sup> | 1.301s | .301s | .130s | |
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| 1000 characters per line (//n//= number of lines): | 1000 characters per line (//n//= number of lines): |
| | //n// | input() | sys.stdin.readline() | sys.stdin.readlines() | | | //n// | input() | sys.stdin.readline() | sys.stdin.readlines() | |
| | 10<sup>4</sup> | .046 | .037 | .033 | | | 10<sup>4</sup> | .046s | .037s | .033s | |
| | 10<sup>5</sup> | .282 | .183 | .143 | | | 10<sup>5</sup> | .282s | .183s | .143s | |
| | 10<sup>6</sup> | 2.728 | 1.430 | 1.723((The ''readlines()'' version is actually slower than ''readline()'' on the largest dataset. It is attempting to store about 1GB in memory here, causing a slowdown, but still faster than ''input()''. | | 10<sup>6</sup> | 2.728s | 1.430s | 1.723s((The ''readlines()'' version is actually slower than ''readline()'' on the largest dataset. It is attempting to store about 1GB in memory here, causing a slowdown, but still faster than ''input()''. |
| )) | | )) | |
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| | The above tests were designed to showcase minimal reading functionality other than temporary storage.((We deliberately avoided additional processing such as typecasts, ''map()'', and ''split()'', as these are non-IO considerations in Python3.)) |
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